System and method for dry forming absorbent cores

ABSTRACT

An apparatus and method for dry forming absorbent cores are disclosed. The apparatus has a rotatable drum having a substantially cylindrical surface. A vacuum surface having one or more holes is located substantially circumferentially around at least a portion of the substantially cylindrical surface. A vacuum chamber is located within the rotatable drum. The vacuum chamber has one or more vacuum passages forming a vacuum zone subadjacent at least a portion of the vacuum surface. A first casing sheet is supplied to overlie the vacuum surface at a first location, and a fibrous material is supplied to overlie the first casing sheet at a second location. A supply of particulate matter is deposited onto the fibrous material at a third location, and a second casing sheet is supplied to overlie the first casing sheet, fibrous material and particulate matter at a fourth location, thereby forming an absorbent core composite.

FIELD OF THE INVENTION

The present invention relates generally to systems and methods formanufacturing absorbent garment cores. More specifically, the presentinvention relates to a system and method for providing precisedisposition of superabsorbent particles and other particulate andfibrous additives into an absorbent core.

BACKGROUND OF THE INVENTION

Disposable absorbent garments such as infant diapers or training pants,adult incontinence products and other such products typically wereconstructed with a moisture-impervious outer backsheet, amoisture-pervious body-contacting inner topsheet, and amoisture-absorbent core sandwiched between the liner and backsheet.

Much effort has been expended to find cost-effective materials forabsorbent cores that display good liquid absorbency and retention.Particles of superabsorbent materials (SAP) in the form of granules,beads, fibers, bits of film, globules, etc., have been favored for suchpurposes. Such SAP materials generally are polymeric gelling materialsthat are capable of absorbing and retaining even under moderate pressurelarge quantities of liquid, such as water and body wastes, relative totheir weight. The SAP particles typically have been distributed within afibrous web of fluffed pulp material, which may comprise natural orsynthetic fibers. Such absorbent structures are commonly referred to asfluff pulp/SAP cores.

Superabsorbent material generally is a water-insoluble butwater-swellable polymeric substance capable of absorbing water in anamount that is at least ten times the weight of the substance in its dryform. In one type of superabsorbent material, the particles may bedescribed chemically as having a back bone of natural or syntheticpolymers with hydrophilic groups or polymers containing hydrophilicgroups being chemically bonded to the back bone or an intimate admixturetherewith. Included in this class of materials are modified polymerssuch as sodium neutralized cross-linked polyacrylates andpolysaccharides including, for example, cellulose and starch andregenerated cellulose that are modified to be carboxylated,phosphonoalkylated, sulphoxylated or phosphorylated, causing the SAP tobe highly hydrophilic. Such modified polymers also may be cross-linkedto reduce their water-solubility.

The ability of a superabsorbent material to absorb liquid is dependentupon the form, position and/or manner in which particles of thesuperabsorbent material are incorporated into the fibrous web of theabsorbent core. Whenever a particle of the superabsorbent material iswetted, it swells and forms a gel. Gel formation can block liquidtransmission into the interior of the absorbent core, a phenomenoncalled “gel blocking.” Gel blocking prevents liquid from rapidlydiffusing or wicking past the “blocking” particles of superabsorbent,causing portions of a partially hydrated core to become inaccessible tomultiple doses of urine. Further absorption of liquid by the absorbentcore must then take place via a diffusion process. This is typicallymuch slower than the rate at which liquid is applied to the core. Gelblocking often leads to leakage from the absorbent article well beforeall of the absorbent material in the core is fully saturated.

Despite the incidence of gel blocking, superabsorbent materials arecommonly incorporated into absorbent cores because they absorb andretain large quantities of liquid, even under load. However, in orderfor superabsorbent materials to function, the liquid being absorbed inthe absorbent structure must be transported to unsaturatedsuperabsorbent material. In other words, the superabsorbent materialmust be placed in a position to be contacted by liquid. Furthermore, asthe superabsorbent material absorbs the liquid it must be allowed toswell. If the superabsorbent material is prevented from swelling, suchas by being tightly constrained within the fibrous web or by pressureexerted by the swelling of adjacent superabsorbent particles, it willcease absorbing liquids.

Adequate absorbency of liquid by the absorbent core at the point ofinitial liquid contact and rapid distribution of liquid away from thispoint are necessary to ensure that the absorbent core has sufficientcapacity to absorb subsequently deposited liquids. Previous absorbentcores have thus attempted to absorb quickly and distribute largequantities of liquids throughout the absorbent core while minimizing gelblocking during absorption of multiple doses of liquid.

Some of the more important performance attributes of an absorbent coreof a diaper (or any other absorbent garment) are functional capacity,rate of absorption, and core stability in use. Absorption under load orAUL is a good measure of functional capacity and the rate at which thatabsorption occurs. AUL is a function of both SAP basis weight (mass perunit area) and the composition of SAP used in the composite.Conventional baby diaper cores that contain only a fibrous web of fluffpulp and a high gel strength SAP typically maintain adequate SAPefficiency if the core contains less than about 50% SAP. Fluff/SAPdiaper cores containing more than 50% SAP generally result in lower SAPefficiency because of gel blocking. Although fluff/SAP cores at greaterthan 50% SAP can provide adequate absorbency, the overall basis weightof the core typically must be increased to compensate for the lowerefficiency of the SAP. Increasing the basis weight decreases theperformance/cost ratio of the absorbent core, making them uneconomical.Also, increased basis weights tend to affect the fit and comfort of thegarment, as well as impacting the packaging and shipping costs.

Attempts to increase the relative weight of SAP by reducing the basisweight of the conventional fluff pulp have resulted in failure becauselow density fluff pulp mats have been unable to withstand the tensileloads placed on them during the manufacturing process. Such cores alsoexhibit poor wet strength, making them unstable during use, and fail toadequately secure the SAP in place. The introduction of relatively highintegrity fibrous structure cores, however, has allowed the basis weightof the fibrous web to be decreased without compromising themanufacturability and wet strength of the absorbent core. Theseabsorbent core structures have improved SAP efficiency and a loweroverall basis weight. Such absorbent cores are disclosed, for example,in U.S. Statutory Invention Registration No. H1,565 to Brodof et al.,which is incorporated by reference herein in its entirety and in amanner consistent with the present invention. These high integrityfibrous structure cores, referred to herein as “tow/SAP” cores or“tow-based” cores, typically use a continuous tow of crimped filaments.The tow may be provided to the absorbent core manufacturer in a compactform and “opened” (i.e., “bloomed” or fluffed up) prior to beingassembled into an absorbent core.

In some cases, the fibrous web of the tow/SAP core may be treated with atackifying agent to adhere the SAP particles to the fibrous web. Inother cases, the SAP particles may be introduced into the fibrous webwithout any adhesive, binder or tackifying agent, such as is disclosedin U.S. Pat. No. 6,068,620 issued to Chmielewski et al., which isincorporated by reference herein in its entirety and in a mannerconsistent with the present invention. Such a construction has beenreferred to as a dry-formed composite (DFC) core. A DFC core may besurrounded by a tissue layer or multiple tissue layers to form a DFClaminate structure that contains the fibrous web and SAP.

A problem with SAP-containing fibrous cores has been to provide the SAPinto the fibrous web in a controlled manner. Typical known processes forcreating a conventional fluff pulp/SAP core use a large forming chamberto blend the SAP with the fluffed pulp, then convey this blend onto adrum or screen by using a vacuum. The drum or screen has forming pocketsthat form the fluff pulp/SAP material into the desired shape and theformed cores then are deposited for integration into absorbent products.Such methods have been found to be inefficient during startup andtransitions in the manufacturing line speed because they require arelatively large amount of time to provide a stabilized mixture of SAPand fluff pulp, leading to the creation of a large number of scrapproducts until stabilization.

Other conventional processes for forming fluff pulp/SAP cores immersethe fluffed pulp in a fluid mixture containing SAP particles, then drythe fluff pulp/SAP mixture before integration into the absorbentarticle. Such vet forming processes typically require more manufacturingsteps and are more expensive than dry forming methods.

Other feeding systems use fixed-size moving mechanical gates thatprovide a uniform amount of SAP to the absorbent core, such as isdisclosed in U.S. Pat. No. 6,139,912 to Onuschak et al., which isincorporated herein by reference in its entirety and in a mannerconsistent with the present invention. Although such devices may besuitable for providing an even flow of SAP or other powdered andparticulate additives to absorbent cores, they rely on relativelycomplex feeding machinery, including a rotary valve that uses apneumatic SAP conveyor to return undistributed SAP back to a supplycontainer. Pneumatic conveyors typically require a relatively long timeto become pressurized and to convey the SAP, causing inefficienciesduring transitional phases, such as when the machine operating speedvaries, such as during start-up and shut-down, or when it is desired tochange the amount of SAP being fed to the core. The additional parts ofsuch feeders may also be expensive and subject to wear and other serviceproblems. Similar devices, having similar deficiencies, are disclosed inU.S. Pat. No. 4,800,102 to Takada, which is incorporated herein byreference in its entirety and in a manner consistent with the presentinvention.

Still other feeding systems use pneumatic particle projectors that usepressurized gas to convey the SAP to the surface of the absorbent core.Such devices are disclosed, for example, in U.S. Pat. No. 5,614,147 toPelley and U.S. Pat. No. 5,558,713 to Siegfried et al., which areincorporated herein by reference in their entirety and in a mannerconsistent with the present invention. Such systems rely on relativelycomplex air conveyors, that may be susceptible to blockage and may notefficiently accommodate as wide a variety of particulate, powder andfibrous materials as other systems due to their relatively small passagesizes. Indeed, it has been found that the compressed air used in suchpneumatic conveyors is often contaminated with oil that may causeblockage, SAP degradation, and other problems. Such systems may alsorequire a relatively long time to stabilize, leading to inefficienciesduring transitional phases.

Other known SAP feeding systems are disadvantageous for a number ofreasons. First, the mixture of fiber and SAP still is subject to localconcentrations and shortages of SAP. Second, these feeding systemstypically can not be controlled accurately enough to provideconcentrations and shortages of SAP when they are desired. Third, suchfeeding systems can not be controlled to accurately provide reduced SAPamounts that are necessary during transitional phases, leading toimproperly loaded cores during those phases of operation.

These are just a few of the disadvantages of the prior art which thepreferred embodiments seek to address. The foregoing description ofcertain material, methods and systems with their attendant disadvantagesin no way is meant to infer that the present invention excludes suchmaterials, methods, and systems. Indeed, certain embodiments of theinvention solve some of the aforementioned disadvantages, yet utilizethe same or similar materials, methods and/or systems.

SUMMARY OF THE INVENTION

It would be desirable to provide an apparatus and method for dry formingabsorbent cores. It also would be desirable for such an apparatus andmethod capable of providing a homogeneous mixture of particulate matterand fibrous material. It also would be desirable for such an apparatusand method to allow relatively precise positioning of regions of highparticulate matter concentrations within the fibrous material to providezoned properties to the absorbent cores. Still further, it would bedesirable for such an apparatus and method to be efficient, easy tooperate, and capable of operating at high line speeds.

In accordance with these and other features of various embodiments ofthe invention, there is provided an apparatus and method for dry formingabsorbent cores. In accordance with one embodiment of the invention, theapparatus has a rotatable drum having a substantially cylindricalsurface. A vacuum surface having one or more holes is locatedsubstantially circumferentially around the substantially cylindricalsurface. A vacuum chamber is located within the rotatable drum, and hasone or more vacuum passages forming a vacuum zone that lies subadjacentat least a portion of the vacuum surface. A first casing sheet supplyoverlies the vacuum surface at a first location, and a supply of fibrousmaterial overlies the first casing sheet supply at a second location. Asupply of particulate matter is deposited onto the supply of fibrousmaterial at a third location, and a second casing sheet supply overliesthe first casing sheet supply, supply of fibrous material and supply ofparticulate matter at a fourth location, thereby forming an absorbentcore composite.

In accordance with other features of preferred embodiments of theinvention, the particulate matter is a superabsorbent polymer, and thefibrous material is tow fibers, preferably a cellulose acetate tow. Inaccordance with another preferred embodiment of the invention, thesupply of opened tow is provided from a tow forming jet, and the supplyof opened tow exits the forming jet at a break angle. In accordance withanother preferred embodiment, the particulate matter is provided from avibratory feeder. In still another preferred embodiment, the mixture ofsuperabsorbent particles and opened tow is at least about 30% by weightsuperabsorbent particles.

In accordance with yet another embodiment of the invention, there isprovided a method for dry forming absorbent cores. The method includesrotating a drum having a substantially cylindrical surface and a vacuumsurface, the vacuum surface comprising one or more holes and beingdisposed substantially circumferentially around the substantiallycylindrical surface. A vacuum is applied to a vacuum chamber locatedwithin the drum. The vacuum chamber has one or more vacuum passagesforming a vacuum zone subadjacent at least a portion of the vacuumsurface. A first casing sheet supply is applied to overlie the vacuumsurface at a first location, and a supply of fibrous material is appliedto overlie the first casing sheet supply at a second location. A supplyof particulate matter is deposited onto the supply of fibrous materialat a third location, and a second casing sheet supply is applied tooverlie the first casing sheet supply, supply of fibrous material andsupply of particulate matter at a fourth location, thereby forming anabsorbent core composite.

In accordance with other features of preferred embodiments of theinventive method, the particulate matter is a superabsorbent polymer,and the fibrous material is opened tow, preferably an opened celluloseacetate tow. In accordance with still other preferred embodiment of theinventive method, the supply of opened tow is provided from a towforming jet and the particulate matter is provided from a vibratoryfeeder.

These and other features of the invention will be readily apparent fromthe Detailed Description that follows, along with reference to thedrawings appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a diaper-type absorbent garment, shown with theeffects of elastics removed for clarity;

FIG. 2 is a cross-sectional view of the garment of FIG. 1, as viewedfrom reference line AA;

FIG. 3 is a partially cut away side view of a system for dry formingabsorbent cores and other structures and machinery according to apreferred embodiment of the present invention, shown in operation and inrelation to a portion of an absorbent garment manufacturing line;

FIG. 4 is a partially cut away view of a feed tray according to apreferred embodiment of the present invention, shown at one end of itsrange of movement and showing the other end of its range of movement indashed lines;

FIG. 5A is a cut away view of a portion of a feed tray according to apreferred embodiment of the present invention;

FIG. 5B is a cut away view of a portion of another feed tray accordingto a preferred embodiment of the present invention;

FIG. 6 is a partially cut away side view of a feed tray, motor and sideplates according to a preferred embodiment of the present invention;

FIG. 7 is an isometric view of the outlet portion of a feed trayaccording to a preferred embodiment of the present invention;

FIG. 8 is an isometric view of the outlet portion of a feed trayaccording to another embodiment of the present invention;

FIG. 9 is an isometric view of a combining drum according to a preferredembodiment of the present invention;

FIG. 10 is a sectional view of the vacuum surface of a combining drumaccording to a preferred embodiment of the present invention, shownoperating with the core composite adjacent the vacuum surface;

FIG. 11 is a partially exploded isometric view of another combining drumaccording to a preferred embodiment of the present invention;

FIG. 12 is an isometric view of yet another combining drum according toa preferred embodiment of the present invention;

FIG. 13 is a cross sectional view of a combining drum assembly accordingto a preferred embodiment of the present invention as viewed from adirection orthogonal to the rotating axis of the combining drum, and asseen from reference line BB of FIG. 14;

FIG. 14 is a cross sectional view of the combining drum assembly of FIG.13, as seen from reference line AA; and

FIG. 15 is a partially cut away view of the combining drum assembly ofFIG. 13, shown with the outer drum partially removed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term “absorbent garment” or “garment” refers togarments that absorb and contain exudates, and more specifically, refersto garments that are placed against or in proximity to the body of thewearer to absorb and contain the various exudates discharged from thebody. A non-exhaustive list of examples of absorbent garments includesdiapers, diaper covers, disposable diapers, training pants, femininehygiene products and adult incontinence products. The term garmentincludes all variations of absorbent garments, including disposableabsorbent garments that are intended to be discarded or partiallydiscarded after a single use (i.e., they are not intended to belaundered or otherwise restored or reused) and unitary disposableabsorbent garments that have essentially a single structure (i.e., donot require separate manipulative parts such as a diaper cover andinsert). As used herein, the term “diaper” refers to an absorbentgarment generally worn by infants and incontinent persons about thelower torso.

The claims are intended to cover all of the foregoing classes ofabsorbent garments, without limitation, whether disposable, unitary orotherwise. These classifications are used interchangeably throughout thespecification, but are not intended to limit the claimed invention. Theinvention will be understood to encompass, without limitation, allclasses of absorbent garments, including those described above.Preferably, the absorbent core is thin in order to improve the comfortand appearance of a garment. The importance of thin, comfortablegarments is disclosed, for example, in U.S. Pat. No. 5,098,423 toPieniak et al., which is incorporated herein by reference in itsentirety and in a manner consistent with the present invention.

Absorbent garments and diapers may have a number of differentconstructions. In each of these constructions it is generally the casethat an absorbent core is disposed between a liquid pervious,body-facing topsheet, and a liquid impervious, exterior facingbacksheet. In some cases, one or both of the topsheet and backsheet maybe shaped to form a pant-like garment. In other cases, the topsheet,backsheet and absorbent core may be formed as a discrete assembly thatis placed on a main chassis layer and the chassis layer is shaped toform a pant-like garment. The garment may be provided to the consumer inthe fully assembled pant-like shape, or may be partially pant-like andrequire the consumer to take the final steps necessary to form the finalpant-like shape. In the case of training pant-type garments and mostadult incontinent products, the garment is provided fully formed withfactory-made side seams and the garment is donned by pulling it up thewearer's legs. In the case of diapers, a caregiver usually wraps thediaper around the wearer's waist and joins the side seams manually byattaching one or more adhesive or mechanical tabs, thereby forming apant-like structure. For clarity, the present invention is describedherein only with reference to a diaper-type garment in which thetopsheet, backsheet and absorbent core are assembled into a structurethat forms a pant-like garment when secured on a wearer using fasteningdevices, although the invention may be used with other constructions.

Throughout this description, the expressions “upper layer,” “lowerlayer,” “above” and “below,” which refer to the various componentsincluded in the absorbent garments of the invention (including thelayers surrounding the absorbent core units), as well as the depictionin the drawings of certain layers or materials that are “above” or“below” one another, are used merely to describe the spatialrelationship between the respective components. The upper layer orcomponent “above” the other component need not always remain verticallyabove the core or component, and the lower layer or component “below”the other component need not always remain vertically below the core orcomponent. Indeed, embodiments of the invention include variousconfigurations whereby the core may be folded in such a manner that theupper layer ultimately becomes the vertically highest and verticallylowest layer at the same time. Other configurations are contemplatedwithin the context of the present invention.

The term “component” can refer, but is not limited, to designatedselected regions, such as edges, corners, sides or the like; structuralmembers, such as elastic strips, absorbent pads, stretchable layers orpanels, layers of material, or the like; or a graphic.

Throughout this description, the term “disposed” and the expressions“disposed on,” “disposing on,” “disposed in,” “disposed between” andvariations thereof (e.g., a description of the article being “disposed”is interposed between the words “disposed” and “on”) are intended tomean that one element can be integral with another element, or that oneelement can be a separate structure bonded to or placed with or placednear another element. Thus, a component that is “disposed on” an elementof the absorbent garment can be formed or applied directly or indirectlyto a surface of the element, formed or applied between layers of amultiple layer element, formed or applied to a substrate that is placedwith or near the element, formed or applied within a layer of theelement or another substrate, or other variations or combinationsthereof.

Throughout this description, the terms “top sheet” and “back sheet”denote the relationship of these materials or layers with respect to theabsorbent core. It is understood that additional layers may be presentbetween the absorbent core and the top sheet and back sheet, and thatadditional layers and other materials may be present on the sideopposite the absorbent core from either the top sheet or the back sheet.

Throughout this description, the expression “fibrous material” denotesany fibrous material that may be used in an absorbent garment, includingwithout limitation, various hardwood and softwood fluff pulps, tissues,cottons, and any other fibrous materials described herein. “Fibrousmaterial” used in the context of the present invention is not intendedto limit the invention to any particular type of fibrous material.

Throughout this description, the expression “tow fibers” relates ingeneral to any continuous fiber. Tow fibers typically are used in themanufacture of staple fibers, and preferably are comprised of syntheticthermoplastic polymers. Usually, numerous filaments are produced by meltextrusion of the molten polymer through a multi-orifice spinneret duringmanufacture of staple fibers from synthetic thermoplastic polymers inorder that reasonably high productivity may be achieved. The groups offilaments from a plurality of spinnerets typically are combined into atow which is then subjected to a drawing operation to impart the desiredphysical properties to the filaments comprising the tow.

A preferred embodiment of the present invention comprises a disposableabsorbent garment 10 of the diaper type, such as shown, for example, inFIG. 1. It should be understood, however, that the present invention isapplicable to other types of absorbent garments. With reference to FIG.1, the diaper 10 according to a first preferred embodiment is shown in arelaxed condition with the effects of the elastics removed for purposesof clarity in the description. The diaper 10 has a generally hourglassshape and can generally be defined in terms of a front waist region 22,a back waist region 24, and a crotch region 26. Those skilled in the artwill recognize that “front” and “back” are relative terms, and theseregions may be transposed without departing from the scope of thepresent invention. Alternatively, the diaper can be configured in agenerally rectangular shape or in a “T” shape. A pair of leg openings 28a, 28 b extend along at least a portion of the crotch region 26. Thediaper preferably comprises a topsheet 2, a backsheet 4, which may besubstantially coterminous with the topsheet 2, and an absorbent core 6disposed between at least a portion of the topsheet 2 and backsheet 4.One or more pairs of leg elastics 8 (three pairs are shown in FIG. 1)may be disposed to extend adjacent to leg openings 28 a, 28 b,respectively. Of course, in other embodiments, the leg elastics 8 may beomitted altogether.

The diaper may further include a front waist elastic system 30 a, a backwaist elastic system 30 b, a fastening system 32 (e.g., tape or othersuitable mechanical fastener) and a waste containment system in the formof waste containment flaps 12 (also known as standing leg gathers).Waste containment flaps 12 (FIG. 2) preferably extend from the frontwaist region 22 to the back waist region 24 along opposite sides of alongitudinal center line or axial center line 60 of the diaper 10, oralternatively only along a portion thereof. The front waist region 22and rear waist region 24 may include ear portions 38, 40 extendingoutwardly from the leg openings 28 a, 28 b.

A variety of backsheet and topsheet constructions and materials areavailable and known in the art, and the invention is not intended to belimited to any specific materials or constructions of these components.The backsheet 4 is of any suitable pliable liquid-impervious materialknown in the art. Typical backsheet materials include films ofpolyethylene, polypropylene, polyester, nylon, and polyvinyl chlorideand blends of these materials. For example, the backsheet can be apigmented polyethylene film having a thickness in the range of 0.02-0.04mm. The moisture-pervious topsheet 2 can be any suitable relativelyliquid-pervious material known in the art that permits passage of liquidtherethrough. Non-woven topsheet materials are exemplary because suchmaterials readily allow the passage of liquids to the underlyingabsorbent core 6. Examples of suitable topsheet materials includenon-woven spunbond or carded webs of polypropylene, polyethylene, nylon,polyester and blends of these materials.

The backsheet 4 and the topsheet 2 preferably are “associated” with oneanother. The term “associated” encompasses configurations whereby thetopsheet 2 is directly joined to the backsheet 4 by affixing thetopsheet 2 directly to the backsheet 4, and configurations whereby thetopsheet 2 is indirectly joined to the backsheet 4 by affixing thetopsheet 2 to intermediate members which in turn are affixed to thebacksheet 4. While the backsheet 4 and topsheet 2 in the preferredembodiment have substantially the same dimensions, they may also havedifferent dimensions.

In addition, the backsheet 4 may be covered with a fibrous, nonwovenfabric such as is disclosed for example in U.S. Pat. No. 4,646,362,which is incorporated herein by reference in its entirety and in amanner consistent with the present invention. Materials for such afibrous outer liner include a spun-bonded nonwoven web of syntheticfibers such as polypropylene, polyethylene or polyester fibers; anonwoven web of cellulostic fibers, textile fibers such as rayon fibers,cotton and the like, or a blend of cellulostic and textile fibers; aspun-bonded-nonwoven web of synthetic fibers such as polypropylene;polyethylene or polyester fibers mixed with cellulostic, pulp fibers, ortextile fibers; or melt blown-thermoplastic fibers, such as macro fibersor micro fibers of polypropylene, polyethylene, polyester or otherthermoplastic materials or mixtures of such thermoplastic macro fibersor micro fibers with cellulostic, pulp or textile fibers.

The backsheet 4 may comprise multiple panels, such as three panelswherein a central poly backsheet panel is positioned adjacent theabsorbent core while outboard non-woven breathable side backsheet panelsare attached to the side edges of the central poly backsheet panel. Thebacksheet may also be formed from microporous poly coverstock for addedbreathability. In other embodiments, the backsheet may be a laminate ofseveral sheets. The backsheet may further be treated to render ithydrophilic or hydrophobic, and may have one or more visual indicatorsassociated with it, such as labels indicating the front or back of thediaper or other characters or colorations. The present invention is notlimited to any particular backsheet 4 material or construction.

The topsheet 2 may be formed from one or more panels of material and maycomprise a laminated sheet construction. In the embodiment of FIG. 1,the topsheet comprises three separate portions or panels. A three-paneltopsheet may comprise a central topsheet panel 2 a (FIG. 2) thatpreferably is formed from a liquid-pervious material that is eitherhydrophobic or hydrophilic. The central topsheet panel 2 a may be madefrom any number of materials, including synthetic fibers (e.g.,polypropylene or polyester fibers), natural fibers (e.g., wood orcellulose), apertured plastic films, reticulated foams and porous foamsto name a few. One preferred material for a central topsheet panel 2 ais a cover stock of single ply non-woven material which may be made ofcarded fibers, either adhesively or thermally bonded, perforated plasticfilm, spunbonded fibers, or water entangled fibers, which generallyweigh from 0.3-0.7 oz./yd² and have appropriate and effective machinedirection and cross-machine direction strength suitable for use as ababy diaper cover stock material, as are known in the art. The centraltopsheet panel 2 a preferably extends from substantially the front waistregion 22 to the back waist region 24 or a portion thereof.

The second and third topsheet panels 2 b, 2 c in this embodiment may bepositioned laterally outside of the central topsheet panel 2 a. Theouter topsheet panels 2 b, 2 c preferably are substantiallyliquid-impervious and hydrophobic, preferably at least in the crotcharea. The outer edges of the outer topsheet panels may substantiallyfollow the corresponding outer perimeter of the backsheet 4. Thematerial for the outer topsheet portions or panels preferably ispolypropylene and can be woven, non-woven, spunbonded, carded or thelike, depending on the application.

An inner region 34 (FIG. 2) of the outer topsheet portions or panels 2b, 2 c preferably is attached by, e.g., an adhesive, to the outer edges36 of the inner topsheet portion or panel 2 a. At the point ofconnection with the outer edges 36 of the inner topsheet portion orpanel 2 a, the inner regions 34 of the outer topsheet portions or panels2 b, 2 c extend upwardly to form waste containment flaps 12. The wastecontainment flaps 12 may be formed of the same material as the outertopsheet portions or panels 2 b, 2 c, as in the embodiment shown. Thewaste containment flaps 12 may also be formed from separate elasticizedstrips of material that are associated with the topsheet, backsheet orboth, or otherwise integrated into the garment.

The waste containment flaps 12 may be treated with a suitable surfactantto modify their hydrophobicity/hydrophilicity or imbue them with skinwellness products as desired. The central topsheet portion or panel 2 amay extend past the connection point with the waste containment flaps 12and even extend to the periphery of the backsheet. Still further, thecentral topsheet portion or panel 2 a could extend fully between theouter topsheet portions or panels 2 b, 2 c and even beyond so that theouter edges 36 of the central topsheet portion or panel 2 a arecoextensive with and sandwiched between the outer topsheet portions orpanels 2 b, 2 c and the backsheet 4.

The waste containment flaps 12 each preferably includes a portion thatfolds over onto itself to form an enclosure. One or more elastic members14 (FIG. 2) may be secured in the enclosure in a stretched condition. Ashas been known at least as long the disclosure of Tetsujiro, JapanesePatent document 40-11543, when the flap elastic 14 attempts to assumethe relaxed, unstretched condition, the waste containment flaps 12 riseabove the surface of the central topsheet portion or panel 2 a. Variousother configurations of topsheets 2 and waste containment systems, suchas flaps 12, are known in the art, and the present invention is notintended to be limited to any particular design for these components.

The waist elastics 30 a, 30 b (FIG. 1) may be similar structures ordifferent to impart similar or different elastic characteristics to thefront and back waist portions 22, 24 of the diaper. In general, thewaist elastics may comprise elastically extensible foam stripspositioned at the front and back waist sections 22, 24. The foam stripsare preferably about 0.50 inches to about 1.50 inches wide and about 3inches to about 6 inches long. The foam strips are preferably positionedbetween the topsheet portions or panels and the backsheet 4.Alternatively, a plurality of elastic strands may be employed as waistelastics rather than foam strips. The foam strips are preferablypolyurethane, but could be any other suitable material that preferablydecreases waist band roll over, reduces leakage over the waist ends ofthe absorbent garment, and generally improves comfort and fit. The frontand back waist foam strips 30 a, 30 b are stretched 50-150%, preferably100% before being adhesively secured between the backsheet 4 andtopsheet 2. Waist elastics are known in the art, and the presentinvention is not limited to the use of a particular waist elasticsystem, or to the inclusion of waist elastics at all.

Each leg opening 28 a, 28 b may be provided with a leg elasticcontainment system S, sometimes referred to as conventional leg gathers.In a preferred embodiment, three strands of elastic threads arepositioned to extend adjacent the leg openings 28 a, 28 b between theouter topsheet portions or panels 2 b, 2 c and the backsheet 4. theselection of appropriate elastics and the construction of leg elasticcontainment systems is known in the art. For example, the leg elastics 8may be ultrasonically bonded, heat/pressure sealed using a variety ofbonding patterns, or glued to the diaper 10.

Various commercially available materials may be used for the legelastics 8 and elastic members 14, such as natural rubber, butyl rubberor other synthetic rubber, urethane, elastomeric materials such asspandex, which is marketed under various names, including LYCRA(DuPont), GLOSPAN (Globe) and SYSTEM 7000 (Fulflex), and so on. Thepresent invention is not limited to any particular elastic.

The fastening system of the diaper 10 may be attached to the back waistregion 24, and preferably comprises tape tabs or mechanical fasteners32. However, any fastening known in the art will be acceptable.Moreover, the fastening system may include a reinforcement patch belowthe front waist portion so that the diaper may be checked for soilingwithout compromising the ability to reuse the fastener. Alternatively,other diaper fastening systems are also possible, including safety pins,buttons, and snaps. Fastening systems are known in the art, and thepresent invention is not limited to using any particular fastening, andmay be constructed without any fastening system at all, such as intraining pant-type garments.

As stated previously, the invention has been described in connectionwith a diaper. The invention, however, is not intended to be limited toapplication only in diapers. Specifically, the present invention may bereadily adapted for use in other absorbent garments besides diapers,including, but not limited to, training pants, feminine hygiene productsand adult incontinence products.

The underlying structure beneath the topsheet 2 may include, dependingon the diaper construction, various combinations of elements, but ineach embodiment, it is contemplated that the absorbent garment willpreferably include an absorbent core 6. For example, an additional layer20 may be disposed between the topsheet 2 and absorbent core 6, as shownin FIG. 2, and/or other additional layers may be disposed between theselayers, or between absorbent core 6 and backsheet 4. The additionallayer 20 or layers may comprise any useful layer known in the art ordeveloped hereafter, such as a fluid acquisition layer, a distributionlayer, an additional fibrous layer optionally containing SAP, a wickinglayer, a storage layer, or combinations and fragments of these layers.Such layers may be provided to assist with transferring fluids to theabsorbent core 6, handling fluid surges, preventing rewet, containingabsorbent material, improving core stability, or for other purposes.Skilled artisans are familiar with the various additional layers thatmay be included in absorbent article, and the present invention is notintended to be limited to any particular type of materials used forthose layers. Rather, the invention encompasses all types of wickinglayers, all types of distribution layers, etc., to the extent that typeof layer 20 is utilized.

The dimensions of additional layer(s) 20 may be the same as or differentfrom the dimensions of the absorbent core 6 and/or topsheet 2 andbacksheet 4. It is preferred that additional layer(s) 20 have a width inthe lateral direction (102) of anywhere from about 10 mm to about 100mm, and preferably from about 25 mm to about 80 mm.

Although the absorbent core 6 depicted in FIG. 1 has a substantiallyrectangular shape as viewed in the plan view, other shapes may be used,such as a “T” shape or an hourglass shape. The absorbent core 6 mayextend into either or both of the front and back waist regions 24, 22.The shape and construction of the absorbent core 6 may be selected toprovide the greatest absorbency in target areas where body fluids aremost likely to strike the diaper 10, which is often referred to as zonedabsorbency. The absorbent core 6 may also comprise a number of layers ofsimilar or different construction. The absorbent core may be associatedwith the topsheet 2, backsheet 4, or any other suitable part of thegarment 10 by any method known in the art, in order to fix the absorbentcore 6 in place.

Generally, in a preferred embodiment, the absorbent core 6 comprisesparticles of super absorbent polymer distributed within a fibrousstructure. Additional fibrous or particulate additives may be disposedWithin the absorbent core 6 to add to the core's strength and SAPefficiency or to otherwise enhance the performance of the garment. Theabsorbent core 6 may be partially or wholly surrounded by a tissue layer16, 18, and other additional layers 20 may be added to provide furtherbenefits. The various components of the absorbent core 6 are nowdescribed in greater detail.

Certain fibrous materials preferably are used to form the fibrousstructure of the absorbent core 6 of the present invention. Thesefibrous materials maintain high SAP efficiencies when the SAPconcentration is in the range of about 50-95%, more preferably about60-90%, and most preferably about 75-85%. For example, the fibrousstructure of the absorbent core 6 may be made with cellulose acetatefibers, rayon fibers, Courtauld's LYOCELL fibers, polyacrylonitrilefibers, surface-modified (hydrophilic) polyester fibers,surface-modified polyolefin/polyester bicomponent fibers,surface-modified polyester/polyester bicomponent fibers, cotton fibers,blends of the foregoing materials, and the like.

Of the foregoing, cellulose acetate tow fibers are the most preferredmaterials for use as the fibrous structure. In addition, rayon,Courtauld's LYOCELL, polyacrylonitrile, cotton fibers and cotton lintershave similar properties to cellulose acetate and are alternativelypreferred. The remaining fibers, surface-modified polyolefin/polyesterbicomponent fibers, and surface-modified polyester/polyester bicomponentfibers are also believed to be effective as a fibrous structure or asfibrous additives. To maintain high SAP concentrations, the weightconcentration of fibrous material forming the absorbent core 6 of theinvention preferably is about 5-50%, more preferably about 10-30%, andmost preferably about 15-25%. Most preferably, the absorbent core 6comprises from about 75-85% SAP and from about 15-25% fibrous structurematerial chosen from the foregoing group.

In accordance with the present invention, improved absorbent articlesare advantageously based upon continuous crimped filament tow, andaccordingly, the central fibrous structure of the core 6 isadvantageously prepared therefrom. This fiber structure has highstructural integrity, and as such, is distinct from a matrix ofdiscontinuous fibers, often described as fluff or fluff pulp, that iscommonly used in the prior art. The high structural integrity enablesthe production of stronger webs than those formed from discontinuousfibers, which in turn are believed to enable the production of thinnerabsorbent pads. In addition, the use of such fibers enables theproduction of ultra low density absorbent cores, when compared toabsorbent cores prepared by dispersing SAP particles in fluff. Thereduction in density is largely attributable to the reduced weight ofthe fibrous structure. Absorbent cores 6 constructed from a blend ofsuch materials and SAP are referred to herein as “tow/SAP” cores or“tow-based” cores.

Beneficially, cellulose ester tow is used to form the fibrous structure.Nonlimiting examples of suitable cellulose esters include celluloseacetate, cellulose propionate, cellulose butyrate, cellulose caproate,cellulose caprylate, cellulose stearate, highly acetylated derivativesthereof such as cellulose diacetate, cellulose triacetate and cellulosetricaproate, and mixtures thereof such as cellulose acetate butyrate. Asuitable cellulose ester will include the ability to absorb moisture,preferably is biodegradable, and is influenced not only by thesubstituent groups but also by the degree of substitution. Therelationship between substituent groups, degree of substitution andbiodegradability is discussed in W. G. Glasser et al, BIOTECHNOLOGYPROGRESS, vol. 10, pp. 214-219 (1994), the disclosure of which isincorporated herein by reference in its entirety.

Continuous filament tow useful in the present invention is beneficiallymoisture-absorbent and biodegradable. Accordingly, cellulose acetate towtypically is preferred for use in the invention. Typically, the denierper fiber (dpf) of the tow fiber will be in the range of about 1 to 9,preferably about 3 to 6, and most preferably about 4. For the sameweight product, filaments of lower dpf may provide increased surfacearea and increased moisture absorption. Total denier of the tow may varywithin the range of about 20,000 to 60,000, depending upon the processused, and is preferably about 35,000. The fibers may have a circular,ovate, rectilinear, or any other cross section. In one embodiment, thefibers have a tri-lobal cross section with an area of about 3.36×10⁻⁶cm². Such a cross-sectional shape may provide improved bendingstiffness, increased wicking, or other beneficial properties.

Tow typically is provided as a relatively dense matrix of fibers, and itis often desirable to “open” (also known as “fluffing” or “blooming”)the tow into a more voluminous cotton-like matrix. To this end, it isparticularly preferred in the invention to use tow having crimpedfilaments, as the crimps aid with opening the tow. The separation offilaments resulting from the opening process advantageously results inincreased available filament surface area for superabsorbent materialimmobilization and increased moisture absorption. Gel blocking also maybe reduced by using crimped tow in the absorbent core 6. As thereforemay be understood, more crimp is typically better, with an excess ofabout 20 crimps per inch being usually preferred. Continuous filamentcellulose ester tow having crimped filaments with about 25 to 40 crimpsper inch is commercially available from Hoechst Celanese Corporation ofCharlotte, N.C.

If desired, an absorbent core 6 of multiple layer thickness may beprovided. To this end, the tow may be, for example, lapped orcrosslapped in accordance with conventional procedures. In this way, asuperabsorbent, absorptive material of a desired weight and/or thicknessmay be provided. The specific weight or thickness will depend uponfactors including the particular end use.

Any superabsorbent polymer (SAP) now known or later discovered may beused in the absorbent core 6, so long as it is capable of absorbingliquids. Useful SAP materials are those that generally arewater-insoluble but water-swellable polymeric substances capable ofabsorbing water in an amount that is at least ten times the weight ofthe substance in its dry form. In one type of SAP, the particles orfibers may be described chemically as having a back bone of natural orsynthetic polymers with hydrophilic groups or polymers containinghydrophilic groups being chemically bonded to the back bone or inintimate admixture therewith. Included in this class of materials aresuch modified polymers as sodium neutralized cross-linked polyacrylatesand polysaccharides including, for example, cellulose and starch andregenerated cellulose which are modified to be carboxylated,phosphonoalkylated, sulphoxylated or phosphorylated, causing the SAP tobe highly hydrophilic. Also included are water swellable polymers ofwater soluble acrylic or vinyl monomers crosslinked with apolyfunctional reactant. Such modified polymers may also be cross-linkedto reduce their water-solubility, and such cross-linked SAPs have beenfound to provide superior performance in some absorbent cores. A moredetailed recitation of superabsorbent polymers is found in U.S. Pat. No.4,990,541 to Nielsen, the disclosure of which is incorporated herein byreference in its entirety. The SAP is preferable selected to providehigh absorbency performance for the particular application. The measureof the SAP's absorbency performance may be evaluated in a number ofways, as will be understood by those skilled in the art. For example, itmay be desirable to provide a SAP having a high measure of saline flowconductivity (SFC), as is described in U.S. Pat. No. 5,562,646 toGoldman et. al, which is incorporated herein by reference in itsentirety and in a manner consistent with the present invention. Ofcourse, the SAP may be selected to provide other properties orcombinations of properties as well.

Commercially available SAPs include a starch modified superabsorbentpolymer available under the trade name SANWET® from Hoechst CelaneseCorporation, Portsmouth, Va. SANWET® is a starch grafted polyacrylatesodium salt. Other commercially available SAPs include a superabsorbentderived from polypropenoic acid, available under the trade name DRYTECH®520 SUPERABSORBENT POLYMER from The Dow Chemical Company, Midland Mich.;AQUA KEEP manufactured by Seitetsu Kagaku Co., Ltd.; ARASORBmanufactured by Arakawa Chemical (U.S.A.) Inc.; ARIDALL 1125manufactured by Chemdall Corporation; and FAVOR manufactured byStockhausen Inc. Still other commercially available SAPs include SA55SX,avalable from Sumitomo Chemical Co. Ltd. of Osaka, Japan, and T7700 andT7200 provided by BASF of Mount Olive, N.J.

The SAP may be provided in any particle size, and suitable particlesizes vary greatly depending on the ultimate properties desired.Preferably, a fine particulate rather than a coarse particulate, is usedin the invention, and preferably a fine particulate that passes throughan about 200 mesh screen is used.

It has been known to prepare absorbent cores comprised of celluloseacetate tow or other polymeric fibers and SAP, as described in U.S.Statutory Invention Registration H1565, and U.S. Pat. Nos. 5,436,066,and 5,350,370, the disclosures of each of which are incorporated byreference herein in their entirety and in a manner consistent with thepresent invention. It was conventional to add tackifying agents,specific size fibers, or specific fibers in combination with fluff, inorder to prepare the absorbent core and immobilize the SAP particles.These additional materials may add to density of the core, or otherwiseadversely affect the overall performance of the absorbent garment madetherefrom. Thus, it is preferred not to use ethylene glycol, tackifyingagents, and very small particulate fibers in the invention, althoughthey may be used to the extent they do not reduce the overallperformance of the garment.

The total basis weights of the absorbent core 6 including fibrousmaterials, SAP, tissue, additional layers, and additives, are anywherefrom about 100 grams per square meter (gsm) to about 1,000 gsm. The mostpreferred total basis weights of the absorbent core 6 are about 500 gsmto about 700 gsm.

Additional particles or fibrous additives may be added to the absorbentcore 6 to help maintain high SAP efficiency, to reduce the cost of thegarment, or to provide other benefits. Fibrous additives may beintroduced as part of the supply of unopened fibers, preferably towfibers, or may be added to the fibers, preferably tow fibers, after ithas been opened. In a preferred embodiment, particulate additivesgenerally may be added to the tow after it has been opened to allowpractical manufacture of the tow and to prevent losses of theparticulate additives during processing.

In one embodiment, about 1-10%, and preferably about 5%, by weight ofthermally bondable synthetic fibers may be added to the absorbent core 6to impart additional wet strength to the laminate. These additive fibersmay improve the stability of the core during use of the diaper. Thepreferred synthetic fibers for such an embodiment arepolyolefin/polyester fibers and polyester/polyester bicomponent fibers.

In another embodiment, the fibrous structure may comprise a combinationof preferred tow materials, such as a blend of cellulose ester andconventional soft or hard wood fibers. Such combinations may be usefulto maintain the improved SAP efficiency available from the crimpedfilament tow-based fibrous structure while providing additionalbenefits. For example, it has been discovered that an absorbent core 6having a 150 g/m² composite comprised of 80% SAP, 10% cellulose acetate,and 10% conventional fluff pulp has a SAP efficiency of about 85%,whereas an absorbent core 6 comprised of 80% SAP and 20% fluff pulp SAPhas an efficiency of about 70%.

The particulate additives that may be added to the absorbent core 6preferably are insoluble, hydrophilic polymers with particle diametersof 100 μm or less. These particulate additives may be chosen to impartoptimal separation of the SAP particles. Examples of preferredparticulate additive materials include, but are not limited to, potato,corn, wheat, and rice starches. Partially cooked or chemically modified(i.e., modifying hydrophobicity, hydrophilicity, softness, and hardness)starches can also be effective. Most preferably, the particulateadditives comprise partially cooked corn or wheat starch because in thisstate, the corn or wheat are rendered larger than uncooked starch andeven in the cooked state remain harder than even swollen SAP. In anyevent, regardless of the particulate additive chosen, one of the manyimportant criteria is to use particulate additives that are hardhydrophilic materials relative to swollen SAP or which are organic orinorganic polymeric materials about 100 microns in diameter. Fibrous andparticulate additives can be used together in these absorbent laminates.Examples of SAP/particulate and SAP/fiber/particulate additives includethose described in, for example, U.S. Pat. No. 6,068,620.

Other particulate or powdered additives also may be deposited within theabsorbent core 6 to provide odor control, skin wellness, and improvedappearance. For example, zeolites, sodium bicarbonate and perfumes maybe added to reduce or mask odors, and titanium dioxide or othercolor-imbuing compounds may be added to provide the absorbent core 6with a more pleasant color.

The absorbent core 6 preferably comprises a tissue wrapping that atleast partially encloses the preferred blended tow and SAP, such asdisclosed in U.S. Pat. No. 6,068,620. The tissue wrapping is useful, forexample, for containing the SAP within the absorbent core 6 andproviding strength to the core during manufacturing and use. In apreferred embodiment, the tissue wrapping comprises first and secondtissue layers 16, 18 that encase the absorbent core 6, and mayoptionally also encase one or more additional layers 20. Preferably, thefirst tissue layer 16 is located generally between the topsheet 2 andthe absorbent core 6, and is hydrophilic and fluid pervious. It is alsopreferred that the second tissue layer 18 be located between thebacksheet 4 and the absorbent core 6 and be hydrophobic and fluidimpervious. The tissue wrapping may also comprise a single tissue layerthat has been folded to encase the absorbent core, and that may be zonetreated to render the portion that forms the lower tissue layer 18hydrophobic and fluid impervious. The tissue layers 16, 18 or the wholecore 6 may be crimped, folded, sealed or bonded to help contain the SAPparticles.

In one embodiment, the fibrous structure and SAP of the absorbent coremay be adhesively or thermally bonded to improve the absorbent core'swet strength and core stability. This, unfortunately, may result inslower than adequate rates of absorption and poor SAP efficiency. Inanother embodiment the SAP and fibrous structure may be hydrogen bondedto additional the tissue layers 16, 18. When a tow-based fibrousstructure having a high concentration of SAP is hydrogen bonded to firstand second tissue layers 16, 18 to form an absorbent core 6, the SAPefficiency is not impaired, wet strength increases, and the first andsecond tissue layers 16, 18 add stability to the core 6 duringmanufacture. It has been found that when the fibrous structure of theabsorbent core 6 is hydrogen bonded using water to the tissue layers 16,18, unexpectedly good “core utilization” is realized. “Core utilization”is the percentage of the total capacity of a core that can be absorbedin a demand absorbency test. This unexpected performance improvement isbelieved to be the result of the beneficial liquid distribution providedby the intimate bond between the fibers of the fibrous structure and thetissue layers 16, 18.

In another preferred embodiment, the first and second tissue layers 16,18 are coated with adhesive prior to being placed on either side of theabsorbent core 6, thereby providing strength to the core and adhesivelyholding a portion of the SAP in place during use. The tissue layers 16,18 may be provided having a width greater than the fibrous structure ofthe absorbent core 6, and the portions of the tissue layers 16, 18extending past either side of the fibrous structure of the core 6 may bebonded to one another to provide further SAP retention capability. Instill another embodiment, if the fibrous structure contains about 1-5%by weight thermally bondable synthetic fibers, bonding to the tissuelayers 16, 18 may be achieved using thermal bonds.

The absorbent core 6 of the present invention may flat or folded when itis fixed in place between the topsheet 2 and backsheet 4. Folded coresmay provide additional performance benefits, such as improved fluidredistribution, greater SAP efficiency, and so on. The absorbent core 6can be folded in any suitable manner, including any and all of thosedisclosed in U.S. Pat. No. 6,068,620. Those skilled in the art willappreciate that the absorbent core 6 can be folded such that theadjacent sides are touching one another, or so that channels are formedin certain areas. For example, the absorbent core 6 can be folded in theform of a “C” where the curled ends may be spaced apart to form achannel there between, and the lower edges of the curled ends may bedisposed adjacent the upper edges of the bottom portion of the foldedarticle. Alternatively, another absorbent material, or another absorbentcore 6 may be disposed in the space formed by the standard “C” fold. Thesame considerations may be given to embodiments having a “G” fold or a“U” fold where the spaces formed by these folds may be filled withanother absorbent material, another absorbent core 6, left open to formfluid handling channels, or the folds may be made tight enough so thatlittle or no space is formed. Other possible arrangements include a “Z”fold, and a pleated absorbent core 6, and other folded shapes, as willbe appreciated by those skilled in the art.

The absorbent core 6 preferably is formed using a dry process. Dryprocesses have numerous benefits over wet processes. For example, in wetprocesses, the core material is typically immersed in a fluid having asuperabsorbent particles mixed or suspended therein, and the corematerial may require additional drying steps and other steps that add tothe complexity and cost of the core forming process. In addition, wetprocesses often require the absorbent core to be manufactured off of themain assembly line. Dry processes typically have lower operating coststhan wet processes because the equipment used in dry processes istypically less complex and can run at higher line speeds. Further, dryforming processes may often be adapted for use directly on the line ofconventional diaper machines. A preferred embodiment of the presentinvention is particularly concerned with using a dry forming process tomanufacture absorbent cores having high concentrations of SAP andrelatively low basis weights, while overcoming or avoiding thedeficiencies of known dry forming processes and machines, as describedelsewhere herein.

One challenge with making absorbent cores having high concentrations ofSAP and relatively low basis weight fibrous structures, as describedabove, is to achieve the desired distribution of SAP within the core. Inmany cases it may be desirable to achieve a uniform distribution of SAPwithin the core to provide the absorbent garment with uniform absorptioncapability. In such a case, not only should the SAP be evenlydistributed along the length and width of the absorbent core, but italso should be properly distributed throughout the thickness of the coreto ensure that the SAP is not subject to gel blocking or otherinefficiencies during-use. It also is desirable to provide a controlledamount of SAP to the core to prevent overuse of the SAP, which typicallyis relatively expensive. It may be further desirable to preciselycontrol the distribution of SAP to provide local regions of the corethat have greater SAP concentrations than others to provide zonedabsorbency. Such concentrations may be along one or more of theabsorbent core's length, width and thickness.

Referring now to FIG. 3, a preferred embodiment of an apparatus andmethod for dry forming composite cores is shown. In the preferredembodiment, a tow supply 302, which may be unopened or partially opened,is provided along a first path to enter a forming jet assembly 304. Thesupply of tow may comprise any material that is desired to be used asthe fibrous structure of the garment's absorbent core 6 and is suitablefor use in the process described herein, such as those that have beendescribed elsewhere herein. Those skilled in the art will appreciatethat if fibers, fluff, or pulp other than tow fibers are used, formingjet assembly 304 would be replaced by a suitable fiber or fluff formingapparatus, as are well known in the art. A preferred material for thetow supply 302 is a supply of cellulose acetate having a basis weight ofabout 50 g/m² to about 100 g/m², and more preferably of about 76 g/m².The tension, speed and path of the tow supply 302 may be adjusted by oneor more movable pulleys 306, guides (not shown) and/or festoons (notshown), as are known in the art.

The tow supply 302 enters the forming jet assembly 304 and is opened inpreparation for being incorporated into absorbent cores. The forming jetassembly 304 comprises a tow inlet 308 at one end into which the towsupply 302 is fed. One or more high velocity jets 310 of air or othergas are projected into the forming jet assembly to impinge upon the towsupply 302 to thereby separate the fibers and “bloom” or open the tow.Preferably, two jets 310 are used and each jet 310 is located proximalto the tow inlet 30S and on opposite sides of the tow supply 302. Eachof the jets 310 preferably comprises a flow of air moving at about 17.5cubic feet per minute through a slit-shaped port that has a length ofabout 3.94 inches and a width of about 0.003 inches. Similar devices foropening tow are known in the art, and disclosed, for example, in U.S.Pat. No. 5,331,976 to St. Pierre, which is incorporated herein byreference in its entirety and in a manner consistent with the presentinvention. Other devices and procedures for opening the tow supply 302may also be used with the present invention, as will be understood bythose skilled in the art.

The opened or “bloomed” tow 312 accumulates within the forming jetassembly 304 as it is being used, and the amount of opened tow 312 beingconsumed may be measured by a level meter 314 (also known as a“dancer”). The level meter 314 may be any suitable electromechanical,optical, or other type of device capable of measuring the amount ofopened tow 312 being consumed. In a preferred embodiment, the levelmeter 314 is a plate that is pivotally attached to a rotary positionsensor (such as a commonly known variable resistance or potentialdevice). As the level of opened tow 312 increases or decreases, theplate pivots up and down, thereby changing the output of the rotaryposition sensor. In a preferred embodiment, the level meter 314 is usedas part of a closed-loop feedback algorithm or an open-loop algorithm tometer the rate at which the tow supply 302 is fed into the forming jetassembly 304, and may be integrated into a control system 320.

The control system 320 may comprise any electrical control apparatusthat may be configured to control one or more variables based on themeasurement of one or more inputs. Although the control system 320 isreferred to herein in the singular, it should be understood that anumber of independent control systems 320 may be used for various partsof the machinery, and these various systems are referred to collectivelyherein as a single control system 320. The control system 320 maycontrol any number of variables and have any number of inputs, and mayuse an open-loop or closed-loop algorithm. Exemplary control systems 320include programmable logic control (PLC) devices having easily usedhuman machine interfaces, as are known in the art. Of course, thecontrol system 320 may simply comprise a human operator that monitorsthe various inputs and adjusts the various system variables.

The opened tow 312 preferably is pulled out of the forming jet assembly304 by a vacuum draw roll 322, such as the combining drum 800 describedelsewhere herein in conjunction with FIG. 8, or a similar drawingdevice. The opened tow 312 exits the forming jet assembly 304 at a towbreak angle Θ_(B), which may be adjusted by altering the position of thevacuum draw roll 322 (or similar device), or, more preferably, byadjusting the height and angle of the forming jet assembly 304 usingadjustable mounts 324. Increasing the tow break angle Θ_(B) increasesthe drag on the opened tow 312 and thereby increases the amount ofstretch that the vacuum draw roll 322 imparts on the opened tow 312.Greater stretch reduces the basis weight of the opened tow 312 that ispulled onto the vacuum draw roll 322. The tow forming jet 304 preferablyis aligned so that its outlet is tangential to the vacuum draw roll 322or slightly above a tangent to the vacuum draw roll 322. In a preferredembodiment, the outlet of the tow forming jet 304 is located at atangent to the vacuum draw roll 322 to about 1 inch above a tangent tothe vacuum draw roll 322. In a more preferred embodiment the outlet ofthe tow forming jet 304 is, less than about 0.75 inches above a tangentto the vacuum draw roll 322, and in a most preferred embodiment, theoutlet of the tow forming jet 304 is located less than about 0.5 inchesabove a tangent to the vacuum draw roll 322.

The tow forming jet's adjustable mounts 324 may be fixed in a desiredposition during machine operation, or may be actively operated by acontrol system 320 during operation in response to measurements of thecore basis weight or other feedback gathered during operation.Mechanical, electromechanical, pneumatic, hydraulic, or other suitableadjusting devices may be used to actuate the adjustable mounts 324, suchas stepper motors, solenoids and hydraulic or pneumatic pistons or rams,and the like. Alternatively, or in addition, the basis weight of theopened tow 312 may be adjusted by increasing or decreasing the speed ofthe vacuum draw roll 322, with faster speeds generally resulting in alower basis weight of the opened tow 312.

After the opened tow 312 exits the forming jet assembly 304, a supply ofsuperabsorbent particles 326 is delivered to the opened tow 312, and thetow/SAP composite is encased between first and second casing sheetsupplies 316, 31S. Alternatively, the tow/SAP composite may be encasedwithin a fold in a single casing sheet. Preferably, as shown in FIG. 3,the opened tow 312 is laid onto a first casing sheet supply 316 beforethe SAP 326 is fed to the opened tow 312 to help contain the SAP 326 andcontrol the SAP distribution, then the second casing sheet supply 318 islaid on the tow/SAP composite to form an absorbent core subassembly thatmay be processed into absorbent garments.

The first and second casing sheet supplies 316, 318 encase the openedtow and SAP composite. The first and second casing sheet supplies 316,318 preferably form the first and second tissue layers 16, 18 of thecompleted garment, but may also form the topsheet 2 and backsheet 4 ofthe absorbent garment 10, or any other layers. The first and secondcasing sheet supplies 316, 318 are preferably wider than the opened tow312 that forms the absorbent core 6, and their side portions arepreferably sealed to one another by bonding or crimping to preventrelease of opened tow 312 and particles of SAP. The absorbent corecomposite 348, comprising the assembly of the first and second casingsheet supplies 316, 318 and the opened tow 312 and SAP 326 core, may befurther processed as it is conveyed through the assembly line forinclusion into absorbent garments 10. For example, in a preferredembodiment, the absorbent core composite 348 is severed into individualabsorbent cores 6, and the severed ends may be crimped or bonded toprevent the SAP 326 from exiting the ends.

In all cases, at least one of the first and second casing sheets 316,318 should be liquid permeable and positioned in the garment to face thewearer's body to allow the flow of fluids into the core 6. The othercasing sheet supply may optionally be liquid impermeable. The liquidimpermeability or permeability of either of the casing sheet supplies316, 318 may be provided by chemical or physical treatment, or by theproper selection of materials, as is known in the art. In an alternativepreferred embodiment, the first and second casing sheets 316, 318 mayboth be formed from a single sheet of material that is folded to encasethe opened tow 312 and SAP 326.

It may be desirable to apply an adhesive to one or both of the first andsecond casing sheet supplies 316, 318 prior joining them with the openedtow 312 or tow/SAP combination. For example, in one preferredembodiment, an adhesive is applied to the entire width of one or both ofthe casing sheet supplies 316, 318 by adhesive applicators 328 beforethey are joined with the opened tow 312 to provide a better bond betweenthe casing sheets 316, 318 and the tow/SAP composite. In such anembodiment, the adhesive may also function to fix a portion of the SAPparticles 326 in place. In another preferred embodiment, the suppliescasing sheet material 316, 318 are wider than the tow/SAP composite, andadhesive is applied along the lateral edges of one or both of the casingsheet supplies to join them to one another, thereby sealing in thetow/SAP composite. Other uses of adhesives will be apparent to thoseskilled in the art based on the teachings provided herein.

A preferred adhesive for these and other embodiments is H2561U hot meltconstruction adhesive, available from Atofindley of Wauwatosa, Wis.Other suitable adhesives, known in the art, may be used provided they donot excessively impair the desired properties of the casing sheetmaterial (as described elsewhere herein), or add excessive stiffness tothe absorbent core 6. For example, other adhesives may include HL-1258by H. B. Fuller Company of St. Paul, Minn.; Findley 2031 and H2587-01 byAto Findley Inc. of Wauwatosa, Wis.; and NS34-5665 by National StarchCo. of Bridgewater, N.J. Other adhesives that may be used include34-578A by National Starch Co. of Bridgewater, N.J. In another preferredembodiment, the adhesive may be selected to impart desired properties tothe casing sheet supplies 316, 318. For example, an adhesive may be usedto render one of the casing sheet supplies 316, 318 fluid impervious,opaque, hydrophobic (or hydrophilic), and so on. the adhesive may alsobe water soluble or have other beneficial properties. Adhesiveapplicators that may be used with the present invention include sprayapplicators, such as those provided by Nordson Corporation of Westlake,Ohio, or other suitable applicators, as are known in the art.

Still referring to FIG. 3, in a preferred embodiment the absorbent corecomposite 348 is assembled in four procedures that take place as thevarious parts of the assembly are pulled onto the rotating vacuum drawroll 322. In the first step, which takes place at location A, the firstcasing sheet supply 316 is drawn onto the vacuum draw roll 322. In thesecond step, at location B, the opened tow 312 is drawn onto the vacuumdraw roll 322 to overlay the first casing sheet supply 316 after beingpulled out of the forming jet assembly 304. In the third step, atlocation C, a supply of SAP 326 is deposited onto the opened tow 312 bythe vibratory feeder 332, as described herein. And in the fourth step,at location D, the second casing sheet supply 318 is brought in tooverlie the first casing sheet supply 316, opened tow 312 and depositedSAP. Those skilled in the art will appreciate that these steps may beperformed using equipment other than that specifically described herein,and may also be performed in various different orders, with some of thesteps being rearranged, omitted or combined, or with additional stepsbeing performed. Such variations are generally within the scope of thepresent invention.

Also in a preferred embodiment, a lay on roll 330 is used to press thesecond casing sheet supply 318 against the tow/SAP composite and thefirst casing sheet supply 316. The lay on roll 330 helps flatten thecore assembly and improves the edge seals between the first and secondcasing sheet supplies 316, 318. The lay on roll 330 may also be equippedto provide ultrasonic, heat, or other bonds between one or more of thefirst and second casing sheets 316, 318 and the tow/SAP composite. Insuch an embodiment, the lay on roll 330 may cooperate with the vacuumdraw roll 322 or other device to create the desired bonds. For example,portions of the lay on roll 330 may form ultrasonic horns, whilecorresponding portions of the vacuum draw roll 332 form ultrasonicanvils that, together, form an ultrasonic bond between the first andsecond casing sheet supplies 316, 318.

The superabsorbent particles preferably are provided by a vibratoryfeeder 33. The vibratory feeder 332 comprises a feed tray 334 that isattached to and driven by a motor 340. The motor 340 vibrates the feedtray 334, moving it back and forth in the direction of vibration V, asindicated by the double-headed arrow in FIG. 3. The feed tray 334 issupplied from above by a hopper 336 by way of a flexible coupling 338that helps isolate the hopper 336 from the movement of the feed tray334. The vibratory feeder is preferably suspended on one or more, andmost preferably three, scales 349 that weigh the vibratory feeder 332and its contents. The vibratory feeder 332 is preferably positioned sothat none of its moving parts, particularly the motor 340 and feed tray334 strike other parts of the machinery during operation.

The hopper 336 is preferably selected to provide consistent flowcharacteristics for a variety of superabsorbent polymers or otherparticulate and fibrous additives. In particular, it is preferred thatthe hopper 336 should flow all of its contents in a regular manner,described as “mass flow,” so that few or none of the particles becomestuck in the hopper 336, and do not experience sudden surges in the flowrate. Mass flow is present when essentially all of the material in thehopper is in motion whenever any material is withdrawn. This type offlow pattern is also described as first-in-first-out flow. In order toprovide the desired mass flow, the hopper 336 is preferably designed toavoid “bridging” (i.e., when particles become lodged in the hopper byforming a “bridge” or arch-like structure that resists flowing), and toavoid “ratholing” (i.e., when a column of particles flows through thecenter of the hopper 336, but those particles along the walls do notflow). When the hopper 336 provides mass flow, it is not necessary toprovide undesirable external forces, which may damage or redistributethe particles, to shake unmoving particles free. Mass flow may beobtained by providing the hopper 336 with relatively smooth interiorwalls and by avoiding the use of shallow flow angles within the hopper336. The design may vary depending on the particulate matter or SAP 326being held in the hopper 336, and it may be desirable to test theproperties of the material, such as the material's slip angle and angleof repose, to obtain a suitable hopper design. The design of mass flowhoppers is generally known in the art, and a skilled artisan will beable to design a suitable hopper without undue experimentation based onthe teachings provided herein.

In one embodiment, the hopper has a capacity of about 1.5 ft³ to about10 ft³, and more preferably about 2.25 ft³ to about 6 ft³, and mostpreferably about 3 ft³. Also in a preferred embodiment, the hopper 336discharges through an outlet having a diameter of about 4 inches toabout 12 inches, and more preferably about 5 to about 9 inches, and mostpreferably about 7 inches. The hopper 336 may be supplied and refilledwith SAP using any device and method known in the art. In a preferredembodiment, the hopper 336 is filled by a screw (or “auger”) typeconveyor that moves SAP from a supply source into the hopper 336. Thedesign of such hoppers 336, conveyors and supply sources is known in theart, and a skilled artisan will be able to provide a hopper 336 for usewith the present invention without undue experimentation based on theteachings provided herein.

In a preferred embodiment, the hopper 336 is derived from a SOLIDSFLOWMODEL 5007 DRY MATERIAL FEEDER. Also in a preferred embodiment, thehopper 336 is supplied and refilled from a SOLIDSFLOW MODEL SBS BULK BAGDISCHARGE STATION using a FLEXICON flexible screw (auger) conveyor,which is controlled by a SOLIDSFLOW MODEL 1200 LOSS-IN-WEIGHTCONTROLLER. All of these devices are available from SolidsFlowCorporation of Fort Mill, S.C.

The vibratory feeder 332 may be suspended from one or more, and mostpreferably three, scales 342 that measure the weight of the vibratoryfeeder 332 and its contents. The scales may be used to calculate theamount of SAP 326 that is being distributed onto the opened tow 312.Such systems are commonly known as “loss-in-weight”systems, as theycontinuously measure the reduction in weight of the vibratory feeder 332as its contents are being emptied. The conveyors and supply sources thatfeed into the hopper 336 may also be suspended on scales so that SAP maybe added to the hopper during operation, while still being able tocalculate the amount of SAP being deposited onto the opened tow 312. Ina preferred embodiment, the loss-in-weight measurements of the scales342 are used with a closed-loop feedback circuit to control the amountof SAP 326 that is deposited onto the opened tow 312. Such a circuit ispreferably integrated into a control system 320 that may control otherfeatures and operation of the vibratory feeder 332 and related devices.The scales 342 may also be used to determine when it is necessary ordesirable to refill the hopper.

The scales 342 are preferably able to read to an accuracy that allowsuseful determination of the amount of SAP being deposited onto theopened tow 312. In a preferred embodiment, the scales 342 read to anaccuracy of about +/−10 grams, and more preferably of about +/−1 gram,and most preferably of about +/−0.1 gram. In a preferred embodiment, thescales 342 comprise strain gauge-type load measurement cells, such asthose available under the designation SOLIDSFLOW MODEL 1000 SCALEASSEMBLY from SolidsFlow Corporation of Fort Mill, S.C. The design,construction, and use of scales suitable for use with the presentinvention is known in the art.

A flexible coupling 338 preferably joins the hopper 336 to the feed tray334. The flexible coupling 338 is used pass SAP or other additives fromthe hopper 336 to the feed tray 334, while simultaneously isolating thehopper 336 from the vibratory movement of the feed tray 334 and motor340. The flexible coupling 338 may comprise any durable flexiblematerial, such as canvas and other cloths, or natural or syntheticrubbers. It is preferred that the flexible coupling does not damp orimpede the desired vibrating motion of the feed tray 334 and motor 340,and thereby impair the ideal SAP feeding. For example, if the flexiblecoupling 338 is too rigid, it will reduce the ability of the motor 340to vibrate the feed tray 334 because it will resist deformation,effectively increasing the mass of the feed tray 334. Also, if theflexible coupling 338 is too elastically resilient, it will tend tostore energy created in it when the feed tray 334 and motor 340 arevibrating, and return this stored energy in an uncontrolled manner(i.e., vibrate on its own) thereby creating additional uncontrolledvibrations in the feed tray 334 and motor 340. It also is preferred thatthe flexible coupling 338 be as light as possible so as to reduce theinertia that must be overcome by the motor 340 during operation. In apreferred embodiment, the flexible coupling 338 comprises a rubbermaterial having a diameter and shape selected to join the outlet of thehopper 336 with the inlet chute 402 of the feed tray 334.

The feed tray 334 and motor 340 preferably are suspended below thehopper 336 by flexible mounts 344 that allow the motor 340 and feed tray334 to move relative to the hopper 336. The flexible mounts 344 maycomprise rods having flexible or pivoting couplings joining them, ateach end, to the hopper 336, motor 340 and feed tray 334. In a preferredembodiment, the flexible mounts 344 are designed to convey a minimalamount of vertical movement or vibration to the hopper 336, which maycause the scales 342 to read inaccurately. In such a preferredembodiment, the flexible mounts 344 may be joined to one or more of thehopper 336, motor 340 and feed tray 334 by a dry or liquid-filledelastomeric bushing or coupling. The design and selection of suchvibration- and movement-damping couplings are known in the art, and askilled artisan will be able to select or produce an appropriatecoupling system based on the teachings provided herein.

Referring now to FIG. 4, the feed tray 434 preferably comprises an inletchute 402 that is attached to the flexible coupling 338 to receive SAP326 from the hopper 336. A pan 404 extends away from the inlet chute 402at a downward angle α to an outlet edge 406 of the feed tray 334. Thepan 404 may also comprise multiple sections that descend at varyingangles. The feed tray 334 preferably is covered along most of its lengthto prevent disturbances of the SAP 326 or other particulate additives.The covered portion preferably terminates at an adjustable gate 408located near the outlet edge 406 of the feed tray 334. The adjustablegate 408 is spaced above the pan 404 and generally divides the feed trayinto an upstream portion from which the SAP 326 flows and a downstreamportion. The adjustable gate 408 may be operated manually, or may beopened and closed by an actuating device, such as an electromechanical,mechanical, pneumatic, or hydraulic device. Such an actuating device mayoptionally be controlled by a control system 320 using a closed-loopfeedback algorithm or open-loop algorithm. Such actuating devices areknown in the art, and a skilled artisan will be able to employ asuitable actuating device without undue experimentation. Of course, inone embodiment the gate may be a fixed gate, rather than an adjustablegate.

In a preferred embodiment, the SAP 326 or other particulate additivematerial exits the feed tray 334 at its outlet edge 406 in acurtain-like stream having a consistent flow rate across its entirewidth. Referring to FIG. 7, the active width W_(A) of the feed tray 334is the width of the portion of the feed tray 334 from which the SAP 326flows (which may be affected by the use of SAP guides 410, as describedelsewhere herein), and generally corresponds to the width of the SAPflow. The active width W_(A) may vary from one application to the next,and may be varied during operation by using, for example actuatedpivoting SAP guides 410 that move together and apart under the controlof a control system 320. Generally, the active width W_(A) preferably isas approximately the same width as the opened tow 312. In one embodimentactive width W_(A) is about 2 inches to about 12 inches, and is morepreferably about 3 inches to about 10 inches, and, in a particularlypreferred embodiment, the active width W_(A) is as about 3.75 inches toabout 4 inches.

In other embodiments it may be desirable to vary the flow rate of theSAP 326 in particular areas to provide zoned absorbency. Referring nowto FIG. 8, the pan 404 may be contoured or shaped to provideconcentrated flows of SAP during operation or to otherwise control theflow of the SAP. For example, in one embodiment the pan 404 may have oneor more depressions 1502 along the outlet edge 406 that effectivelyincrease the downward angle α at the depressions 1502. In such anembodiment, the SAP 326 may tend to funnel into the depressions 1502,and those portions of the opened tow 312 that pass beneath thedepressions 1502 should receive a relatively high concentration of SAP326. In another embodiment, the pan 404 may have troughs 1504 thatextend below the adjustable gate 408, effectively increasing the heighth of the adjustable gate 408 at those points to increase the flow rateof SAP through the troughs 1504. Such troughs 1504 may extend to theoutlet edge 406 to additionally act as depressions 1502, as describedabove. Other variations in the outlet edge 406 and pan 404 geometry willbe apparent to those skilled in the art based on the teachings providedherein.

In one embodiment, the feed tray 434 may have more than one inlet chute402 so that a number of different supplies of SAP may be fed into it.The supplies of SAP may comprise different types of SAP that are blendedor isolated from one another using internal baffles and guides. In suchan embodiment, for example, one type of SAP may be distributed to thelateral sides of the opened tow 312, and another type of SAP may bedistributed to the central region of the opened tow 312. Othervariations and uses of a feed tray 334 having multiple inlet chutes 402will be apparent to those skilled in the art based on the teachingsprovided herein.

SAP guides 410, comprising vertical or angled strips of material,optionally may be integrated into the feed tray 334 on either side ofthe adjustable gate 408 to serve a number of purposes. The SAP guidesare preferably attached to the pan 404, but may also be attachedelsewhere to the feed tray 334 or to other objects. In a preferredembodiment, the guides contain the lateral movement of the SAP 326 sothat it falls only in a center region of the opened tow 312. In anotherpreferred embodiment, the SAP guides 410 isolate the flow of SAP 326from turbulent airflow around the feed tray 334 to provide more even SAPdistribution. The SAP guides 410 may be proximal to the outlet edge 406,as shown in FIG. 4, or may be located elsewhere on the pan 404. The SAPguides 410 may also be used to isolate or blend different supplies ofSAP. In one embodiment, the SAP guides 410 may also comprise additionalvertically stacked layers, in addition to the pan 404, that may containseparate flows of SAP. In a preferred embodiment, the SAP guides 410 arespaced apart by about 3.75 inches to about 4 inches to provide about a3.75 inch to about 4 inch wide flow of SAP.

Referring now to FIGS. 5A and 5B, the feed tray 334 operates on theprinciple that particulate solids within them, such as SAP 326, willrest at their angle of repose until disturbed by vibrations induced bythe motor 340. This principle of operation is more fully disclosed inU.S. Pat. No. 3,973,703 to Peschl, which is incorporated by referenceherein in its entirety and in a manner consistent with the presentinvention (hereafter referred to herein as “Peschl”). It should beunderstood that, although the inventors provide various theories on themodes of operation of the vibratory feeder 332, the invention is notintended to be limited to these or other modes or theories of operation.

It has been found that the flow of the SAP 326 generally may beinfluenced by the properties of the SAP, the downward angle α of the pan404, the rate of vibration of the motor 340, the trailing distance d ofthe pan 404, and the height of the adjustable gate 408. In theembodiment shown in FIG. 5A, the feed tray 334 is shown at rest, withthe SAP 326 being contained within the feed tray 334. In the embodimentof FIG. 5A, the downward angle α is greater than the angle of repose ofthe SAP 326, and so any SAP remaining along the trailing distance d ofthe pan 404 slides off the pan 404′ after the motor 340 stops vibrating.The remaining SAP 326 is caught behind a bridge 502 of SAP that forms byfriction between the particles of SAP, cohesion between the SAPparticles, or both. The adjustable gate height h may be adjusted toprovide ideal SAP containment and control. Raising the adjustable gate408 generally provides a greater SAP flow rate for a given motorvibration frequency, while lowering the adjustable gate 408 generallyprovides the opposite result. The adjustable gate height h preferably isadjusted to ensure that a bridge 502 forms promptly after the motor 340stops vibrating the feed tray 334 to stop the flow of SAP 326 as quicklyas possible.

The flow rate of the SAP generally follows the vibration rate of themotor 340, and stops flowing almost immediately upon shut down of themotor 340. Generally, faster motor vibration rates provide greater SAPflow rates and slower motor vibration rates provide a slower SAP flowrate. There is little or no appreciable time delay between changes inthe motor frequency and the flow rate of the SAP 326, so the vibratoryfeeder 332 provides relatively accurate control of the SAP flow,especially when compared to known methods of distributing SAP ontoopened tow 312 or fluff pulp.

It should be noted that SAP remaining on the trailing distance d of thepan 404 may continue to flow at an uncontrolled rate after the motorfrequency changes, but such lag time has not been found to cause anappreciable detriment to the device's ability to accurately deposit SAP326 onto the opened tow 312. If a detriment is found, however, thetrailing distance d may be reduced to make the SAP flow rate follow themotor frequency variations more closely. Reducing the trailing distancemay also increase the flow rate of the SAP for a given motor frequencyand adjustable gate height h, as is explained in more detail in Peschl.In one embodiment, the trailing distance may be reduced to zero, and theoutlet edge 406 even may be within the upstream portion of the feed tray334 (i.e., the adjustable gate 408 may be located beyond the outlet edge406).

In a more preferred embodiment, shown in FIG. 5B, the downward angle αmay be less than the SAP's angle of repose and slip angle (i.e., theangle at which the SAP 326 will slide down the surface of the pan 404),so that when the feed tray 334 is at rest the SAP remaining along thetrailing distance d stays on the pan 404. In such an embodiment, theaforementioned lag between SAP flow and motor frequency changesassociated with the SAP located in the trailing distance d may bereduced.

Referring back to FIG. 4, it has been found that the feed tray's outletedge 406 should be located as close as possible to the vacuum draw roll322. Reducing the offset distance c between the outlet edge 406 and thevacuum draw roll 322 provides a number of benefits. In particular,minimizing the offset distance c allows the SAP to fall onto the openedtow 312 as quickly as possible, minimizing any redistribution ordiffusion of SAP 326 that may be caused during a longer fall byturbulent air flowing around the feed tray 334 and by interactionbetween the SAP particles 326. Reducing the offset distance c alsodecreases the lag time between changes in motor speed 340 and changes inthe amount of SAP 326 being distributed to the opened tow 312. In apreferred embodiment, the offset distance is about 025 inches to about4.00 inches, and more preferably about 0.375 inches to about 1.00 inch,and most preferably about 0.50 inches.

The minimum value for the offset distance c may be affected by machineoperating tolerances, such as to prevent contact between the open tow312 or the vacuum draw roll 322 and the vibrating feed tray 334, or byother factors, such as the tolerances of the casing sheet supplies 316,318 and opened tow 312. For example, in a preferred embodiment, theoffset distance c is at least about 0.50 inches to allow passage ofclumped aggregations of opened tow 312, that may be present duringstartup and during other operating conditions.

In a preferred embodiment that may be used with a variety of SAPs, thedownward angle α, as measured relative to horizontal, is about 10degrees to about −5 degrees, and more preferably about 12 degrees toabout 30 degrees, and most preferably about 15 degrees. Also in apreferred embodiment, the adjustable gate height h is about 0.10 inchesto about 1.00 inches, and more preferably about 0.125 inches to about0.75 inches, and most preferably about 0.25 inches to about 0.50 inches.Also in a preferred embodiment, the trailing distance d is about 0.25inches to about 8 inches, and more preferably about 2 to about 6 inches,and most preferably about 4 inches. Also in a preferred embodiment, theinlet chute 402 has a diameter of about 4 inches to about 12 inches, andmore preferably about 5 to about 9 inches, and most preferably about 7inches. In a preferred embodiment, the feed tray '334 may be derivedfrom a SOLIDSFLOW MODEL 5000 DRY MATERIAL FEEDER, available fromSolidsFlow Corporation of Fort Mill, S.C.

Referring now to FIGS. 6 and 7, the feed tray 334 preferably is equippedwith side plates 602 that help isolate the SAP 326 and opened tow 312from lateral airflow and may help contain the lateral movement of SAP326 after it exits the feed tray 334. Such lateral airflow and otherairflow may disturb the desired distribution of SAP onto the opened tow312. The side plates 602 are preferably oriented approximately parallelto the machine direction of the opened tow 312 (i.e., within about 20degrees of parallel) and sized to substantially reduce or block air fromflowing laterally into the area beneath the feed tray 334. Preferably, afirst edge 604 of each side plate 602 is located proximal to the vacuumdraw roll 322 (or other similar drawing device); and a second edge 606of each side plate 602 is located proximal to the forming jet assembly304. The side plates 602 are preferably shaped and sized so that they donot strike any other parts of the machine as they are vibrated back andforth. A third edge 608 of each side plate 602 preferably is adapted toconform to the second casing sheet supply 318 to help prevent lateralairflow from above the feed tray from encroaching upon the supply of SAP326. In such an embodiment, it also may be desirable for the top edge610 of the adjustable gate 408 to be proximal to the second casing sheetsupply 318 to further reduce the amount of air that flows in topotentially disturb the SAP 326. The SAP guides 410 may also have anedge 612 contoured to be adjacent to the second casing sheet supply 318to further inhibit the development of undesirable airflow near the SAP326. The side plates 602 preferably may be adjusted in at least thevertical direction, as indicated by the double-headed arrow in FIG. 6.In other embodiments, the side plate 602 may be attached to somethingother than the feed tray 334, but in such embodiments, care should betaken to prevent the moving feed tray 334 from striking the side plates602 during operation.

Referring back to FIG. 4, the motor 340 is used to initiate and modulatethe flow of SAP 326 out of the feed tray 334. The motor 340 vibrates thefeed tray 334 by moving it back and forth in the direction of vibrationV, as indicated by the double-headed arrow in FIG. 4. In a preferredembodiment, both the pitch p and frequency of the motor 340 may beadjusted to modulate the flow of SAP 326. It has been found thatincreasing the motor's pitch p (i.e., the distance traversed by themotor during each cycle) generally increases the SAP flow rate, andvice-versa. Also, as noted before, it has been found that increasing themotor's frequency generally also increases the SAP flow rate, andvice-versa.

The effectiveness of the motor 340 and amount of control provided by themotor 340 are affected by the weight and rigidity of the feed tray 334.If the feed tray 334 is too heavy, its inertia will resist the forcesimparted upon it by the motor 34 d, and the motor 340 may not be able toaccelerate and decelerate it back and forth to create the desired pitchp distance or frequency vibrations. If the feed tray 334 is not rigidenough, it will flex as the motor 340 imparts forces on it. As the feedtray 334 flexes, it absorbs the energy that was intended to move thefeed tray 334 and does not accurately follow the path intended by themotor 340. The energy absorbed by a flexible feed tray 334 may bereleased in the form of undesirable variations in the intended pitch pand frequency of vibration. It has been found that it is generallydesirable to make the feed tray 334 as light and as rigid as possible inorder to provide the greatest amount of control of the SAP flow.

In a preferred embodiment, the motor 340 is coupled to the feed tray 334through a coupling 412. In order to provide accurate transmission of themotor's vibrations to the feed tray 334, the coupling 412 should berigid in the vibration direction V, and the coupling 412 preferably hasa box-like shape or C-shape. Also in a preferred embodiment, the inletchute 402, which may comprise a relatively large open space that may besusceptible to undesirable flexing, is reinforced with a structuralmember, such as a tubular brace 414 aligned in the vibration directionV. In an embodiment in which the inlet chute has a diameter of about 7inches it has been found that a tubular brace 414 of about 1 inchdiameter is suitable to reduce undesirable flexure in the inlet chute402 without adversely affecting the flow of SAP through the inlet chute.In other embodiments, in which the inlet chute 402 contains baffles orother internal flow-directing or flow-controlling structures, thesestructures may also serve to increase the feed tray's rigidity, makingit unnecessary to reinforce the inlet chute 402.

As noted before, the motor 340 and feed tray 334 are suspended beneaththe hopper 336 by flexible mounts 344 that allow both the motor 340 andthe feed tray 334 to move independently of the hopper 336. As such, asthe motor 340 vibrates the feed tray 334 back and forth, the motor 340itself may also move back and forth. In a preferred embodiment, the massof the motor 340 is significantly greater than the combined mass of thefeed tray 334 and the SAP 326 contained therein, and so the movement ofthe motor 340 will be insignificant relative to the movement of the feedtray 334. In such an embodiment, the motor's pitch p will be almostentirely converted into movement of the feed tray 334 (as is shown inFIG. 4). If, however, the motor 340 does experience a significant amountof movement, more of the pitch p will be converted into the motor'smovement, and less of the pitch will result in movement of the feed tray334. This reduction in the movement of the feed tray 334 may result inless effective SAP distribution and control. If it is found that themovement of the motor negatively affects the SAP distribution andcontrol, the motor's movement may be restricted, or the pitch p may beincreased to increase the effective movement of the feed tray 334. Othermeasures may also be taken to counteract such negative affects. Thoseskilled in the art will be able to measure or calculate the movement ofthe motor 340 and feed tray 334 and make accommodations in the design ofthe apparatus for such movements using the teachings provided herein.

In a preferred embodiment, the motor 340 comprises an electromagneticvibrator, such as those supplied by Eriez, Corporation of Erie, Pa. asModel Number 30A, part number 3N-56743. Such a motor may be selected tobe driven by any available power source, such as a 115 volt, 60 Hz powersource. The motor may also require specific support or drive hardwareand software, such as an Eriez VTF signal following controller boardthat is supported by and AB SLC 0-20 mA analog card, available fromAllen-Bradley Company of Milwaukee, Wis. Other motors 340 may also beused, such a rotary motor that is configured to provide cyclical lateralmovement or vibrations to the feed tray 334. Other useful motors 340include pneumatic, magnetic, electric and hydraulic actuators, and thelike, as long as they can provide the necessary forces to vibrate thefeed tray 334 at the desired pitch p and frequency. Electromagneticvibrators are preferred, as they typically provide relativelycontrollable movement and consume less energy than other devices.

In one embodiment that should be suitable for dispensing a variety ofSAP materials, the motor 340 may be operated from a standstill (zero Hz)up to about 430 Hz, and more preferably up to about 520 Hz, and mostpreferably up to about 600 Hz. In a preferred embodiment that should besuitable for dispensing a variety of SAP materials, the frequency isapproximately constant, and the flow rate of the particulate matter iscontrolled by modulating the motor's pitch. In such a preferredembodiment, the motor frequency is about 60 Hz, and the pitch p of themotor variable between about 0.01 inches to about 0.125 inches, and morepreferably about 0.02 inches to about 0.10 inches, and most preferablyabout 0.04 inches to about 0.08 inches. Such adjustments may beobtained, for example, by varying the voltage of the motor between about0 and about 90 volts.

Such a vibratory feeder 332 may be adapted to provide a high volume ofSAP flow, and may be used at relatively high manufacturing line speeds.It is anticipated that a vibratory feeder produced according to apreferred embodiment of the present invention may be used with anassembly line producing diapers at a rate in excess of 600 products perminute. The vibratory feeder 332 preferably can feed superabsorbentpolymer or other additives at a rate of about 10,000 grams per minute(g/min) to about 20,000 g/min, and more preferably at a rate of about12,500 g/min to about 17,500 g/min, and most preferably at a rate ofabout 15,000 g/min. In a preferred embodiment, the hopper 336 is fed bya screw-type conveyor or other conveyor that has a capacity to maintaina useful level of SAP 326 in the vibratory feeder 332. The conveyor mayhave a feed rate that is less than the maximum feed rate of thevibratory feeder 332, so long as the average feed rate of the vibratoryfeeder 332 does not exceed the average feed rate of the conveyor.

Superabsorbent polymers and other particulate additives can berelatively expensive, and so it is often desirable to minimize theamount of SAP that is placed in the core and to “zone” such additivesonly where they are most beneficial for the final product. Such zoningis also particularly beneficial in tow-based absorbent cores because thelack of fluff pulp in such cores may reduce the overall wickingcapability of the core, making it more important to place the SAP closerto the location where fluid is likely to strike the garment. In apreferred embodiment, the motor 340 is controlled by a control system320 to provide a desirable distribution of SAP 326 into the opened tow312. In one preferred embodiment, such a control system 320 may be usedto operate the motor 320 to deposit a steady stream of SAP 326 onto theopened tow 312 to provide a uniform opened tow/SAP mixture in theabsorbent cores that are ultimately formed by the process. In anotherpreferred embodiment, the control system may cyclically increase anddecrease the pitch p and/or frequency of the motor 340 to deposit apulsating supply of SAP 326 to the opened tow 312, thereby providing theabsorbent cores with targeted concentrations of SAP that provide thegarment 10 with zoned absorbency. Preferably, the control system 320uses a closed-loop feedback method that considers various factors indetermining how much SAP to distribute at any given moment.

In a preferred embodiment, the control system 320 is provided withinformation about how fast the assembly line is running by using, forexample, a tachometer 346 on the vacuum draw roll 322 or by any othersuitable line speed measuring device (See FIG. 3). By integrating such aline speed measuring device into the control system 320, the controlsystem 320 may be programmed to increase or decrease the pitch p orfrequency of the motor 340 to vary the SAP flow rate as the productmanufacturing rate changes, thereby providing all of the products withthe proper amount of SAP, regardless of the assembly line speed. Such acapability provides a lower rate of product rejection duringtransitional phases, thereby improving the overall efficiency of themanufacturing process.

In another preferred embodiment, the output of the scales 342 isintegrated into the control system 320. By considering the weight of theSAP being distributed, as measured by the scales 342, the control system320 may programmed to modulate the motor 340 to accurately distributeSAP at the desired flow rate. In such an embodiment, the control system320 may also accommodate for deviations in the flow characteristics ofthe SAP particles to continue to provide an even flow, such as byincreasing the vibration rate if it is found that the SAP is not flowingas rapidly as expected, and vice-versa. Such deviations may be caused bytypical variations in the shape, size, humidity, density, or otherfeatures of the SAP, or may be caused when a different SAP product isused in a machine that was originally set up for another type of SAP orset up for a SAP provided by a different supplier.

A closed-loop feedback control system 320 may also be programmed to stopdistributing SAP in the event that a fault is detected in the processingline. For example, if a fault detection circuit tied into the controlsystem 320 determines that one or more products will be defective uponcompletion, the flow of SAP may be stopped so that the defectiveproducts will not receive SAP. In such an embodiment, it may bedesirable to produce the absorbent cores of the garments as late aspossible in the manufacturing process in order to detect as many defectsas possible before preparing the absorbent core 6 for each product.

In one embodiment, a SAP concentration detection device 350 (FIG. 3) maybe integrated into the control system 320 to provide further detectionand control capabilities to the control system 320. The concentrationdetection device 350 may be located to measure the amount and/orlocation of SAP in the assembled absorbent core composite 348. If theamount of location of the SAP is not present as desired, theconcentration detection device 350 may signal this to the control system320 so that appropriate corrections in the SAP feed rate may be made.Those skilled in the art are capable of designing or utilizing asuitable SAP concentration detection device 350 using the guidelinesprovided herein.

The flow rate of the SAP may also be controlled by a control device 320by actively adjusting the height h of the adjustable gate 408 duringoperation. As noted before, the adjustable gate 408 may be raised andlowered during operation to increase and decrease, respectively, theflow rate of the SAP 326. Such adjustments may also be made to provide acyclically fluctuating amount of SAP to the opened tow 312 to createtargeted regions of relatively high SAP concentration for zonedabsorbency. In such an embodiment, the control device 320 may operatethe adjustable gate 408 in conjunction with the scales 342, tachometer346, concentration detection device 350, or other sensors to provideclosed-loop feedback control of the SAP flow. A suitable actuationdevice for cyclically raising and lowering the adjustable gate 408preferably does not cause excessive vibrations or other movements thatmay cause the scales 342 to read inaccurately.

Referring now to FIG. 9, it has been found that a “combining drum”-typevacuum draw roll 800 may be advantageously used in conjunction withvibratory feeders 332, such as those described herein, or,alternatively, with other SAP feed devices and methods, such as thosethat are known in the art. The combining drum 800 is characterized inthat several or all of the parts that eventually form the absorbent core6 of the garment 10 are assembled in a continuous motion around all orpart of the combining drum's circumference. In a preferred embodiment,the combining drum 800 combines the first casing sheet supply 316,opened tow 312, SAP 326 and second casing sheet supply 318 (i.e.,various constituent parts of the core composite 348, which may, ofcourse, include other parts) in a substantially continuous operation asthey are conveyed by the combining drum 800. Each of the parts may beconveyed to the combining drum 800 separately and then joined togetherinto an integrated structure, or alternatively, some of the parts may bejoined to one another prior to contact with the combining drum 800. Forexample, an additional layer 20 may be affixed to either side of one orboth of the first and second casing sheet supplies 316, 318 before thesupply is provided to the combining drum 800.

As noted before, a preferred combining process has been generallydescribed elsewhere herein with reference to Locations A, B, C and D ofFIG. 3. The operation of the combining drum 800 described herein isrelatively simple compared to many known core-forming apparatus, and maybe adapted to operate at high line speeds. For example, it isanticipated that the combining drum 800 may be adapted to operate withan assembly line producing in excess of 600 diapers per minute.

In a preferred embodiment the combining drum 800 has a generallycylindrical surface 802 with a vacuum surface 804 forming acircumferential belt on the cylindrical surface 802. The vacuum surface804 comprises one or more holes 806 through which a vacuum is applied tothe various parts of the core composite 348. The holes 806 in the vacuumsurface 804 may be formed by any means known in the art, such asdrilling, machining, casting and so on. In a preferred embodiment, theholes 806 have a diameter of about 0.0625 inches to about 0.75 inches,and more preferably of about 0.125 inches to about 0.625 inches, andmost preferably of about 0.25 inches to about 0.50 inches. Also in apreferred embodiment, the holes may be spaced from one another by acenter-to-center distance of about 0.10 inches to about 1.00 inch. Theholes may be spaced in a rectilinear array, as staggered rows, or in anyother pattern that conveys the desired amount of vacuum. The vacuumsurface 804 also may comprise any other relatively rigid foraminousstructure, such as one or more mesh screens or removable perforatedplates that are affixed to openings in the cylindrical surface 802. In apreferred embodiment, the combining drum 800 may also comprise landingareas 808 on either side of the vacuum surface 804 which may be treatedto enhance their ability to grip the first and second casing layersupplies 316, 318. A vacuum is applied to the combining drum 800 througha vacuum port 810.

Referring now to FIG. 10, there is shown a sectional view of the vacuumsurface 804 region of a combining drum 800 as is appears just aftercombining the first casing sheet supply 316, opened tow 312, SAP 326 andsecond casing sheet supply 318 into an integrated core composite 348.The width W₁ of the vacuum surface 804 (as measured in a directionparallel to the rotational axis of the combining drum 800) preferablycorresponds approximately to the width of the opened tow 312 and to thewidth of the portion of the feed tray 334 from which SAP 326 isprovided. The first and second casing sheet supplies 316, 318 arepreferably wider than the opened tow 312, and their excess width islocated in side areas 902 that overlie the landing areas 808. The firstand second casing sheet supplies 316, 318 preferably are joined to oneanother in their side areas 902 by adhesive bonding, other methodsdescribed elsewhere herein or by other methods known in the art. Asnoted elsewhere, a lay on roll 330 may be used to help join the firstand second casing sheet supplies 316, 318 by use of pressure, crimpingnodules, and the like.

In a preferred embodiment, the vacuum surface 804 is recessed in thecylindrical surface by a depth y of less than about 0.50 inches, andmore preferably by less than about 0.10 inches, and most preferably byabout 0.030 inches. It has been found that having a slight increase inthe diameter of the combining drum 800 on either side of the vacuumsurface 804 (i.e., a recessed vacuum surface 804) helps keep the firstcasing sheet supply 316 stretched across the combining drum 800 duringoperation.

The vacuum surface width W₁ may be selected to provide certain benefitsto the garment into which the core composite 348 is being integrated. Inone embodiment, the core composite may be integrated into the garment ina flat state, in which case it may be desirable to make the vacuumsurface width W₁ and the width of the opened tow 312 equal to thedesired width of the garment's absorbent core 6. However, the corecomposite 348 may be stretched, folded, or otherwise resized duringmanufacture, in which case the vacuum surface width W₁ should becorrespondingly adjusted. In a preferred embodiment, the core composite348 is folded at least once before being integrated into the garment.Folded absorbent cores have been discussed in more detail elsewhereherein. In a preferred embodiment, the vacuum surface width W₁ is about1.75 inches to about 12 inches, and more preferably about 2.75 inches toabout 10 inches, and most preferably about 3.75 inches. In order toreduce SAP loss during core formation, the vacuum surface width ispreferably slightly narrower (about 0.10 inches on either side) than thewidth of the supply of opened tow 312 to promote a slight inwardmigration of SAP away from the side areas 902.

As noted before, it has been a continuing challenge to provide thedesired distribution of SAP within the absorbent cores 6 of absorbentgarments 10. It has been found that a combining drum 800 as describedherein may be beneficially used to help provide such desired SAPdistributions. Cellulose acetate opened tow 312 and other types of lowdensity fibrous opened tow structures allow a relatively large amount ofair to pass through them compared to conventional fluff pulp materials,and the location of the SAP 326 may be effectively controlled bymodulating the amount and position of the vacuum applied to theSAP/opened tow mixture. It has been found that the distribution of theSAP can be more easily controlled with tow/SAP cores than with fluff/SAPcores. As air passes through the opened tow 312 into the vacuum itconveys the SAP 326 through the fibrous structure, and the SAP particles326 generally tend to concentrate more densely at areas having a highvacuum. Also, as the vacuum is increased, the SAP particles 326generally move closer to the surface of the opened tow 312 that isadjacent the combining drum 800. The degree to which the SAP migratestowards the high vacuum areas may also be affected by the duration oftime that the vacuum is applied to the SAP 326. The vacuum also helpsprevent SAP 326 from escaping out of the opened tow 312 duringmanufacturing. It has been found that a desirable mixture of SAP 326within the opened tow 312 and reduced SAP loss may be produced using avacuum of about 2.50 inches of water to about 20 inches of water, andmore preferably of about 3.75 inches of water to about 12.5 inches ofwater, and most preferably of about 5.0 inches of water. The vacuum maybe pre-set or may be manually or actively controlled by a control system320 using an open-or closed-loop feedback system.

In addition to being useful for providing a homogeneous dispersion ofSAP 326 in the opened tow 312, a combing drum 800 as described hereinmay also be used to accomplish various other desirable SAP distributionpatterns. In one embodiment, the vacuum level may be modulated toprovide a desirable depth of SAP penetration throughout the opened tow312 or only in discrete areas of the opened tow 312. In otherembodiments, the combining drum 800 may be adapted to provide machinedirection (MD) and cross-machine direction (CD) zoning of the SAPparticles 326 that provide the garment 10 with zoned absorbency. Themachine direction is the direction in which a part or assembly movesduring processing, and the cross-machine direction is perpendicular tothe MD. The machine direction generally corresponds to the longitudinaldimension 100 of the fully-assembled garment 10 (see FIG. 1), and thecross machine direction corresponds to the lateral dimension 102 of thegarment, however other relationships may also be used and are within thescope of the present invention.

Referring now to FIG. 11, regions of high SAP concentration, and thusgreater absorbency, may be provided in the MD and CD by making thevacuum surface 804 with particularly designed target regions 1002 thatconvey a greater amount of vacuum to portions of the opened tow 312.Such target regions 1002 may have larger holes and/or a greaterconcentration of holes in those areas where a greater concentration ofSAP 326 is desired. The larger amount of open space provided in suchregions will allow a greater amount of airflow into the vacuum, and thuscause a greater amount of SAP to migrate to those areas. For example, inthe embodiment of FIG. 11, the region 1004 has a greater concentrationof larger holes, which should provide a SAP concentration in the portionof the core composite 384 adjacent region 1004. The particular patternof SAP concentration may be adjusted by making each of the targetregions 1002 from a removable plate 1006 having the desired holepattern. Substitute plates 1006 may be easily machined to providedifferent hole patterns and zoned absorbency patterns.

In another embodiment, shown in FIG. 12, the vacuum surface 804 may beseparated into discrete target regions 1102, which may have varyingwidths, to provide zones of high and low MD and CD SAP concentrations.

In an embodiment in which the combining drum 800 has target regions1002, 1102 for providing zoned absorbency, the combining drum diameterD₁ should be selected so that the corresponding parts of each targetregions 1002, 1102 are spaced from one another around the circumferenceof the combining drum 800 by a distance corresponding to the absorbentcore length X₁. By using such a spacing, each target region 1002, 1102will create a targeted zone of SAP that will be properly located in eachabsorbent core 6 that is cut from the core composite 348.

It should be understood that by providing a distance betweencorresponding parts of each target region 1002, 1102 that isapproximately equal to a core length X₁, the circumference of thecombining drum 800 will be sized to equal a whole number multiple of thecore length X₁. At a minimum, the circumference can equal one corelength X₁, but in such an embodiment, the various parts of the corecomposite 348 will be in contact with the vacuum for relatively littletime, which may lead to inadequate SAP distribution or other formingproblems. Smaller diameter drums may also be subject to greatervibration. These problems may become exacerbated when the vacuum drum800 is used with higher speed assembly lines. Problems may also be existwith larger drum diameters. For example, the manufacturing tolerancesfor a larger diameter drum may be less precise. In addition, as the sizeof the drum increases the amount of startup waste may increase,particularly if a greater amount of vacuum is required for the largerdrum, leading to longer vacuum stabilization times. Larger drums thatrequire greater amount of vacuum also may require more power to producethe necessary vacuum. It will be understood that these considerationsalso apply to embodiments of the invention in which the combining drum800 does not have target regions 1002, 1102, such as in the embodimentdepicted in FIG. 9.

It is preferred, therefore, that the drum diameter D₁ be selected sothat the drum's circumference is large enough that the parts of the corecomposite 348 are in contact with the vacuum long enough to properlydistribute the SAP without excessive vibrations, but small enough toprovide the required precision and a minimal amount of startup waste. Ithas been found that in a preferred embodiment, the diameter D₁ isselected so that the circumference is equal to between three and sevencore lengths X₁. In a preferred embodiment, the combining drum 800(whether it has target regions 1002, 1102 or not) has a diameter D₁ ofabout 6 inches to about 28 inches, and more preferably of about 9 inchesto about 20 inches, and most preferably of about 12 inches. In thisembodiment, the number of wasted cores caused by vacuum hysteresis orother startup-related issues has been found to be about 5 products perstartup, as compared to up to about 50 products per startup withconventional core forming processes. It has also been found thatproviding the necessary vacuum to such a combining drum 800 requiresabout 10 horsepower to 20 horsepower, whereas conventional core formingsystems require up to about 400 horsepower, and so a significant powersavings is provided.

Referring now to FIGS. 13 through 15, a preferred embodiment of thecombining drum is shown in which the combining drum 800 may beconfigured to apply a vacuum to the parts of the core composite 348 onlythrough a portion of the drum's rotation. The combining drum 800 of apreferred embodiment comprises an outer drum 1202 that is positioned torotate about a fixed inner drum 1204 by, for example, being affixed toan axle 1208 that passes through rotary bearings 1210 in the inner drum1204. Such bearings 1210 may be equipped to reduce or prevent theleakage of the vacuum through them. A vacuum is applied to the space1206 inside the inner drum by a vacuum port 810. The vacuum is conveyedto the outer drum's vacuum surface 804 by way of one or more passages1212 through the inner drum 1204 that are preferably located subadjacentthe path of the vacuum surface 804 of the outer drum 1202 to maximizethe strength of the vacuum applied through the vacuum surface 804. Itwill be understood by those skilled in the art that the inner drum 1204may be replaced by any vacuum chamber having one or more passages 1212that convey a vacuum to a location subadjacent all or part of the vacuumsurface 804.

Only those portions of the vacuum surface 804 that are immediatelyadjacent the passages 1212 receive a vacuum, so the duration andlocation of the vacuum's application may be modified by changing thesize, number, or location of the passages 1212. Referring specificallyto FIG. 14, the passages 1212 may be positioned through an arc of theinner drum 1204 that defines a vacuum zone Θv. The leading edge of thevacuum zone 1302 is preferably located proximal to the point at whichthe first casing sheet supply 316 contacts the combining drum, which isdesignated as Location A in FIG. 3. The trailing edge of the vacuum zone1304 is preferably located beyond (as the drum rotates) the point atwhich the second casing sheet supply 318 contacts the combining drum800, which is designated as Location D in FIG. 3. Referring now to FIG.15, it can be seen that those portions of the vacuum surface 804 thatare not adjacent the passages 1212 are effectively cut off from the pullof the vacuum. After the core composite 348 passes the trailing edge ofthe vacuum zone 1304 and reaches this blocked-off area it is releasedfrom the vacuum's hold and conveyed to other parts of the assembly line.

The size of the vacuum zone Θv may vary depending on where the variousparts are desired to be assembled to form the core composite 348. In apreferred embodiment, the vacuum zone Θv is about 45 degrees to about180 degrees, and more preferably is about 90 degrees to about 160degrees, and most preferably is about 140 degrees.

Various devices may be employed with the combining drum 800 to modulatethe location and amount of vacuum applied to the core composite 348. Inone embodiment, shown in FIG. 14, internal sleeves 1306 or other valvingmechanisms may be used to adjust the points at which the vacuum zone Θvbegins and ends. In another embodiment, shown in FIG. 13, other internalsleeves 1214 or other valving mechanisms may be used to narrow or widenthe width of the vacuum zone Θv, thereby effectively narrowing andwidening the width W₁ of the vacuum surface 804. In still anotherembodiment, an internal sleeve or other valving mechanism may be used toreduce the vacuum level within all or part of the inner drum 1204. Anyof such sleeves and valving mechanisms may be actuated by a controlsystem 320 under the guidance of an open- or closed-loop feedbacksystem. Greater or lesser amounts of vacuum may also be applied indiscrete portions of the vacuum zone Θv. Other designs will be obviousto one skilled in the art based on the teachings provided herein.

A combining drum 800, as described herein, may be used with any SAPfeeding device that deposits SAP onto opened tow or other fibrousmaterials. The embodiments of the combining drum 800 described hereinhave been found to be particularly useful when used in conjunction withthe vibratory feeder 332 as described herein.

The present invention offers several advantages over previous SAPdepositing systems. In particular, the vibratory feeder 332 providesimproved control over the volume and placement of the SAP 326 in thefiber, preferably the opened tow 312, allowing greater control over theSAP distribution (and zoned absorbency) during transitional phases, suchas during machine startup, stopping and other speed changes, leading tofewer rejected products during such times. In addition, the vibratoryfeeder 332 and combining drum 800 provide improved SAP penetration intothe fiber, preferably the opened tow 312 or other core material and animproved ability to selectively position the SAP to provide desirablezoned absorbency. The vibrator feeder 332 and combining drum 800 alsoprovide easier operation, as the various features of each device may beintegrated into a control system 320. Stull further, the vibratoryfeeder 332 and combining drum 800 are relatively simple and reliabledevices that require little maintenance or cleaning, thereby reducingthe operating cost of the machine. Another advantage of the vibratoryfeeder and combining drum 800 is that they may be operated at high linespeeds without detriment to the product quality. Other benefits will beapparent to those skilled in the art based on the teachings providedherein.

Other embodiments, uses, and advantages of the invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. Thespecification should be considered exemplary only, and the scope of theinvention is accordingly intended to be limited only by the followingclaims and equivalents thereof.

1-48. (canceled)
 49. A method for dry forming an absorbent core composite comprising: rotating a drum comprising a substantially cylindrical surface and a vacuum surface, the vacuum surface comprising one or more holes and being disposed substantially circumferentially around at least a portion of the substantially cylindrical surface; applying a vacuum to a vacuum chamber that is disposed within the drum and that has one or more vacuum passages, thereby forming a vacuum zone subadjacent at least a portion of the vacuum surface; applying a first casing sheet supply to overlie the vacuum surface at a first location; applying a supply of fibrous material to overlie the first casing sheet supply at a second location; depositing a supply of particulate matter onto the supply of fibrous material at a third location; and applying a second casing sheet supply to overlie the first casing sheet supply, supply of fibrous material and supply of particulate matter at a fourth location, thereby forming an absorbent core composite.
 50. The method of claim 49, wherein the supply of particulate matter is a supply of superabsorbent particles.
 51. The method of claim 49, wherein the supply of fibrous material comprises a supply of cellulose acetate tow.
 52. The method of claim 49, wherein the first casing sheet supply and second casing sheet supply comprise tissue.
 53. The method of claim 49, further comprising applying the vacuum to the particulate matter to relatively homogeneously distribute the supply of particulate matter throughout the supply of fibrous material.
 54. The method of claim 49, further comprising applying the vacuum to the particulate matter to distribute the supply of particulate matter into relatively highly concentrated regions within the supply of fibrous material.
 55. The method of claim 49, further comprising pressing the second casing sheet supply against the first casing sheet supply with a lay on roll located proximal to the fourth location.
 56. The method of claim 49, wherein the third location is positioned between the second location and the fourth location.
 57. The method of claim 49, wherein the third location is not positioned between the second location and the fourth location.
 58. A method for dry forming an absorbent core composite comprising: rotating a drum comprising a substantially cylindrical surface and a vacuum surface, the vacuum surface comprising one or more holes and being disposed substantially circumferentially around at least a portion of the substantially cylindrical surface; applying a vacuum to a vacuum chamber that is disposed within the drum that has one or more vacuum passages, thereby forming a vacuum zone subadjacent at least a portion of the vacuum surface; applying a first casing sheet supply to overlie the vacuum surface at a first location; applying a supply of opened tow from a tow forming jet to overlie the first casing sheet supply at a second location; depositing a supply of particulate matter onto the supply of opened tow at a third location using a vibratory feeder; and applying a second casing sheet supply to overlie the first casing sheet supply, supply of opened tow and supply of particulate matter at a fourth location, thereby forming an absorbent core composite.
 59. An absorbent garment comprising: a topsheet; a backsheet; and an absorbent core disposed between the topsheet and the backsheet comprising fibrous material and particulate matter; wherein the particulate matter is distributed in the fibrous material using the apparatus of claim
 1. 60. The absorbent article of claim 59, wherein the fibrous material comprises an opened tow of cellulose acetate and the particulate matter comprises superabsorbent particles.
 61. An absorbent article comprising: a topsheet; a backsheet; and an absorbent core disposed between the topsheet and the backsheet comprising fibrous material and particulate matter; wherein the particulate matter is distributed in the fibrous material using the method of claim
 45. 62. The absorbent article of claim 61, wherein the fibrous material comprises an opened tow of cellulose acetate and the particulate matter comprises superabsorbent particles. 